Nonaqueous electrolyte for secondary battery and nonaqueous-electrolyte secondary battery employing the same

ABSTRACT

An object is to provide a nonaqueous electrolyte and a nonaqueous-electrolyte secondary battery which have excellent discharge load characteristics and are excellent in high-temperature storability, cycle characteristics, high capacity, continuous-charge characteristics, storability, gas evolution inhibition during continuous charge, high-current-density charge/discharge characteristics, discharge load characteristics, etc. The object has been accomplished with a nonaqueous electrolyte which comprises: a monofluorophosphate and/or a difluorophosphate; and further a compound having a specific chemical structure or specific properties.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/594,513, filed on Jan. 6, 2010, which is a 35 U.S.C. §371national stage patent application of international patent applicationPCT/JP2008/056803, filed Apr. 4, 2008, which claims priority to thefollowing Japanese patent applications: JP 2007-099274, filed Apr. 5,2007; JP 2007-111931, filed Apr. 20, 2007; JP 2007-111961, filed Apr.20, 2007; JP 2007-116442, filed Apr. 26, 2007; JP 2007-116445, filedApr. 26, 2007; and JP 2007-116450, filed Apr. 26, 2007.

TECHNICAL FIELD

The present invention relates to a nonaqueous electrolyte for secondarybattery and to secondary battery employing the electrolyte. Moreparticularly, the invention relates to nonaqueous electrolyte which isfor use in lithium secondary battery and contain a specific ingredient,and to lithium secondary battery employing the electrolyte.

BACKGROUND ART

<Nonaqueous Electrolyte 1 and Nonaqueous-Electrolyte Secondary Battery1>

With the recent trend toward size reduction in electronic appliances,secondary batteries are increasingly required to have a higher capacity.Attention is hence focused on lithium secondary batteries(nonaqueous-electrolyte secondary batteries), which have a higher energydensity than nickel-cadmium batteries and nickel-hydrogen batteries.

The electrolytes used in lithium secondary batteries are nonaqueouselectrolytes prepared by dissolving an electrolyte such as LiPF₆, LiBF₄,LiClO₄, LiCF₃SO₃, LiAsF₆, LiN(CF₃SO₂)₂, or LiCF₃(CF₂)₃SO₃ in anonaqueous solvent such as a cyclic carbonate, e.g., ethylene carbonateor propylene carbonate, an acyclic carbonate, e.g., dimethyl carbonate,diethyl carbonate, or ethyl methyl carbonate, a cyclic ester, e.g.,γ-butyrolactone or γ-valerolactone, an acyclic ester, e.g., methylacetate or methyl propionate, or the like.

First, various investigations have been made on nonaqueous solvents andelectrolytes in order to improve the battery characteristics includingload characteristics, cycle characteristics, and storability of suchlithium secondary batteries. For example, patent document 1 includes astatement to the effect that when an electrolyte containing avinylethylene carbonate compound is used, the decomposition of thiselectrolyte is minimized and a battery excellent in storability andcycle characteristics can be fabricated. Patent document 2 includes astatement to the effect that when an electrolyte containingpropanesultone is used, recovery capacity after storage can beincreased.

However, incorporation of such compounds has had a problem that althoughthe incorporation has the effect of improving storability and cyclecharacteristics to some degree, a coating film having high resistance isformed on the negative-electrode side and this, in particular, reducesdischarge load characteristics.

<Nonaqueous Electrolyte 2 and Nonaqueous-Electrolyte Secondary Battery2>

Secondary, various investigations have been made on nonaqueous solventsand electrolytes for use in those nonaqueous electrolytes in order toimprove the battery characteristics including load characteristics,cycle characteristics, and storability of those lithium secondarybatteries. For example, use of a nonaqueous solvent having a higherpermittivity and a lower coefficient of viscosity has variousadvantages, e.g., the resistance of the electrolyte can be reduced to alow value, as described in non-patent document 1. Furthermore, thatnonaqueous solvent is thought to be capable of improving infiltrationinto the positive and negative electrodes. Use of that nonaqueoussolvent is hence preferred.

However, solvents having a heteroelement-containing functional group(group constituting a framework) other than a carbonyl framework, suchas ether compounds and nitrile compounds, which are one kind ofpreferred solvents from those standpoints have the following drawback.These solvents are electrochemically decomposed by an oxidation reactionat the positive electrode or by a reduction reaction at the negativeelectrode and are hence difficult to use. Practically, carbonic estersor carboxylic acid esters, such as enumerated above as examples, areused in combination. These solvents have a carbonyl group and haveexcellent oxidation resistance/reduction resistance.

On the other hand, patent document 1 includes a statement to the effectthat when an electrolyte containing a vinylethylene carbonate compoundis used, the decomposition of this electrolyte is minimized and abattery excellent in storability and cycle characteristics can befabricated. Patent document 2 includes a statement to the effect thatwhen an electrolyte containing propanesultone is used, recovery capacityafter storage can be increased.

However, incorporation of such compounds has had the following problemalthough the incorporation has the effect of improving storability andcycle characteristics to some degree. When these compounds are used inorder to sufficiently improve characteristics, a coating film havinghigh resistance is formed on the negative-electrode side and this, inparticular, reduces discharge load characteristics. Especially whenthose solvents which have a heteroelement-containing functional group(group constituting a framework) other than a carbonyl framework andhave a high permittivity and a low viscosity are used, there has been aproblem that the preferred characteristics are not imparted.

The desire for higher performances in nonaqueous-electrolyte secondarybatteries is growing more and more, and it is desired to attain variouscharacteristics including high capacity, high-temperature storability,continuous-charge characteristics, and cycle characteristics on a highlevel.

<Nonaqueous Electrolyte 3 and Nonaqueous-Electrolyte Secondary Battery3>

Thirdly, various investigations have been made on nonaqueous solventsand electrolytes in order to improve the battery characteristicsincluding load characteristics, cycle characteristics, and storabilityof such lithium secondary batteries. For example, patent document 3includes a statement to the effect that when an electrolyte containing aphosphinic acid ester is used, a battery inhibited from deteriorating inbattery performance during high-temperature storage or during continuousdischarge can be fabricated. Patent document 4 proposes a secondarybattery which has an excellent life in charge/discharge cycling at avoltage exceeding 4.2V and is fabricated using an electrolyte containingan organic compound having two or more cyano groups.

Especially when a battery is in the state of being continuously chargedin which a slight current is permitted to always flow therethrough tokeep the battery in a charged state in order to compensate for theself-discharge of the battery, then the electrodes are always in thestate of having high activity. Because of this, the battery is apt tosuffer accelerated deterioration in capacity or gas evolution is apt tooccur due to the decomposition of the electrolyte. In particular, in thecase of a battery having high capacity, there is a problem that sincethe space within this battery has a small volume, the internal pressureof the battery increases considerably even when a slight amount of a gasis evolved due to the decomposition of the electrolyte. With respect tocontinuous-charge characteristics, not only reduced capacitydeterioration but also the inhibition of gas evolution are stronglydesired.

However, the electrolytes containing the compounds described in patentdocument 3 and patent document 4 have been insufficient in theinhibition of gas evolution during continuous charge and in theinhibition of battery characteristics deterioration, although theelectrolytes have the effect of improving cycle characteristics andstorability to some degree.

<Nonaqueous Electrolyte 4 and Nonaqueous-Electrolyte Secondary Battery4>

Fourthly, various investigations have been made on nonaqueous solventsand electrolytes in order to improve the battery characteristicsincluding load characteristics, cycle characteristics, and storabilityof such nonaqueous-electrolyte batteries or to enhance the safety ofsuch batteries during heating or at the time of short-circuiting. Forexample, sulfolane combines a high permittivity and high electrochemicaloxidation stability even in nonaqueous solvents and a boiling point ashigh as 278° C., which is higher than those of ethylene carbonate andpropylene carbonate. Sulfolane can hence be expected to contribute to animprovement in battery safety when used as a solvent. However, sulfolanehas a melting point as high as 28° C. and there has been a problem thata battery employing sulfolane as a main solvent has impairedlow-temperature characteristics. Furthermore, it is known that sulfolanehas poor compatibility with graphite-based negative electrodes and thatuse of sulfolane as a main solvent results in a charge/dischargecapacity lower than a theoretical capacity.

For example, patent document 5 discloses that in anonaqueous-electrolyte secondary battery employing the electrolytedescribed therein, the electrolyte can be prevented from solidifying atlow temperatures by using a mixed solvent composed of sulfolane andethyl methyl carbonate.

Patent document 6 discloses that when sulfolane and γ-butyrolactone areused as main solvents and vinylethylene carbonate and vinylene carbonateare added thereto, then a coating film of satisfactory quality which hashigh lithium ion permeability is formed on the surface of thegraphite-based negative electrode and an improved initialcharge/discharge efficiency is obtained.

<Nonaqueous Electrolyte 5 and Nonaqueous-Electrolyte Secondary Battery5>

Fifthly, many reports have been made on the addition of variousadditives to electrolytes for the purpose of improving initial capacity,rate characteristics, cycle characteristics, high-temperaturestorability, low-temperature characteristics, continuous-chargecharacteristics, self-discharge characteristics, overcharge-preventiveproperties, etc. For example, to add 1,4,8,11-tetraazacyclotetradecanehas been reported as a technique for improving cycle characteristics(see patent document 7).

However, the desire for higher performances in nonaqueous-electrolytesecondary batteries is growing more and more, and it is desired toattain various characteristics including high capacity, high-temperaturestorability, continuous-charge characteristics, and cyclecharacteristics on a high level. For example, the prior-art techniquedisclosed in patent document 7, which is regarded therein as effectivein improving cycle characteristics, has had a problem that thistechnique, when used alone, results in considerable gas evolution duringcontinuous charge and in a considerable decrease in recovery capacityafter a test, as will be shown later in a Reference Example.

<Nonaqueous Electrolyte 6 and Nonaqueous-Electrolyte Secondary Battery6>

Sixthly, various investigations have been made on nonaqueous solventsand electrolytes in order to improve the battery characteristicsincluding load characteristics, cycle characteristics, and storabilityof such lithium secondary batteries. For example, patent document 1includes a statement to the effect that when an electrolyte containing avinylethylene carbonate compound is used, the decomposition of thiselectrolyte is minimized and a battery excellent in storability andcycle characteristics can be fabricated. Patent document 2 includes astatement to the effect that when an electrolyte containingpropanesultone is used, recovery capacity after storage can beincreased.

However, incorporation of such compounds has had a problem that althoughthe incorporation has the effect of improving storability and cyclecharacteristics to some degree, a coating film having high resistance isformed on the negative-electrode side and this, in particular, reducesdischarge load characteristics.

-   Patent Document 1: JP-A-2001-006729-   Patent Document 2: JP-A-10-050342-   Patent Document 3: JP-A-2004-363077-   Patent Document 4: JP-A-7-176322-   Patent Document 5: JP-A-2000-012078-   Patent Document 6: JP-A-2004-296389-   Patent Document 7: JP-A-9-245832-   Non-Patent Document 1: Kikan Kagaku Sōsetsu, No. 49, p. 108

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

<Nonaqueous Electrolyte 1 and Nonaqueous-Electrolyte Secondary Battery1>

An object of the invention, which has been achieved in view of thebackground art described above, is to provide a nonaqueous electrolytefor secondary batteries which has excellent discharge loadcharacteristics and is excellent in high-temperature storability andcycle characteristics.

<Nonaqueous Electrolyte 2 and Nonaqueous-Electrolyte Secondary Battery2>

Another object of the invention, which has been achieved in view of thebackground art described above, is to provide another nonaqueouselectrolyte which has excellent discharge load characteristics and isexcellent in high-temperature storability and cycle characteristics.

<Nonaqueous Electrolyte 3 and Nonaqueous-Electrolyte Secondary Battery3>

Still another object of the invention, which has been achieved in viewof the background art described above, is to provide a nonaqueouselectrolyte for secondary batteries which is excellent in cyclecharacteristics, storability, gas evolution inhibition during continuouscharge, and battery characteristics.

<Nonaqueous Electrolyte 4 and Nonaqueous-Electrolyte Secondary Battery4>

However, the recent desire for higher performances in batteries isgrowing more and more, and it is desired to attain high capacity, highoutput power, high-temperature storability, cycle characteristics, highsafety, etc. on a high level.

In a nonaqueous-electrolyte secondary battery employing the electrolytedescribed in patent document 5, the reversibility of electrode reactionsin initial charge/discharge was insufficient. This battery was henceinsufficient in charge/discharge capacity and charge/dischargeefficiency (see Comparative Example 1 for Nonaqueous Electrolyte 4). Onthe other hand, a nonaqueous-electrolyte secondary battery employing theelectrolyte described in patent document 6 has had the followingdrawbacks. γ-butyrolactone, which is used as a main solvent in theelectrolyte, has a coefficient of viscosity at 25° C. as high as 1.73mPa·s, which is higher than those of low-molecular acyclic carbonatesused as main solvents in common electrolytes (e.g., dimethyl carbonate,0.59 mPa·s; diethyl carbonate, 0.75 mPa·s; ethyl methyl carbonate, 0.65mPa·s). Because of this, the electrolyte as a whole had a highcoefficient of viscosity and was unsatisfactory in charge/dischargeefficiency at a high current density. In addition, γ-butyrolactone in acharged state has poor thermal stability and the battery has had aproblem concerning charge/discharge characteristics after storage at ahigh temperature such as 85° C. (see Comparative Example 2 forNonaqueous Electrolyte 4 and Comparative Example 3 for NonaqueousElectrolyte 4).

Consequently, a further object of the invention is to eliminate theproblem that high-current-density charge/discharge characteristicsdecrease when a nonaqueous electrolyte containing a cyclic sulfonecompound is used and to provide a nonaqueous electrolyte capable ofreconciling high battery performance with high safety. Still a furtherobject is to provide a nonaqueous-electrolyte battery employing theelectrolyte.

<Nonaqueous Electrolyte 5 and Nonaqueous-Electrolyte Secondary Battery5>

Still further objects of the invention, which has been achieved in viewof the background art described above, are to provide a nonaqueouselectrolyte which maintains high capacity and imparts satisfactorycontinuous-charge characteristics and to provide anonaqueous-electrolyte secondary battery.

<Nonaqueous Electrolyte 6 and Nonaqueous-Electrolyte Secondary Battery6>

Still a further object of the invention, which has been achieved in viewof the background art described above, is to provide a nonaqueouselectrolyte for secondary batteries which has excellent discharge loadcharacteristics and is excellent in high-temperature storability andcycle characteristics.

Means for Solving the Problems

<Nonaqueous Electrolyte 1 and Nonaqueous-Electrolyte Secondary Battery1>

The present inventors diligently made investigations in view of theproblems described above. As a result, they have found that a nonaqueouselectrolyte which contains at least one carbonate having a halogen atomand to which a specific compound has been added can have excellentdischarge load characteristics and can retain satisfactoryhigh-temperature storability and satisfactory cycle characteristics.Invention 1 has been thus completed.

Namely, invention 1 resides in nonaqueous electrolyte which is anonaqueous electrolyte for use in a nonaqueous-electrolyte secondarybattery comprising a negative electrode and a positive electrode whichare capable of occluding and releasing ions and a nonaqueouselectrolyte, and the nonaqueous electrolyte comprises: an electrolyteand a nonaqueous solvent, wherein the nonaqueous solvent comprises: acarbonate having a halogen atom; and a monofluorophosphate and/or adifluorophosphate.

Invention 1 further resides in nonaqueous-electrolyte secondary battery1 which is a nonaqueous-electrolyte secondary battery comprising anegative electrode and a positive electrode which are capable ofoccluding/releasing lithium ions and a nonaqueous electrolyte, whereinthe nonaqueous electrolyte is the nonaqueous electrolyte descried above.

<Nonaqueous Electrolyte 2 and Nonaqueous-Electrolyte Secondary Battery2>

The inventors diligently made investigations in view of the problemsdescribed above. As a result, they have found that a nonaqueouselectrolyte to which a specific compound has been added can haveexcellent discharge load characteristics and retains satisfactoryhigh-temperature storability and satisfactory cycle characteristics evenwhen a solvent which has a high permittivity and a low coefficient ofviscosity and has a heteroelement-containing functional group other thana carbonyl group has been used therein. Invention 2 has been thuscompleted.

Namely, invention 2 resides in nonaqueous electrolyte 2 which is anonaqueous electrolyte mainly comprising an electrolyte and a nonaqueoussolvent dissolving the electrolyte, and the nonaqueous electrolytecomprises: a compound which is liquid at 25° C., has a permittivity of 5or higher and a coefficient of viscosity of 0.6 cP or lower, and has agroup constituting a heteroelement-containing framework (excludingcarbonyl group); and further a monofluorophosphate and/or adifluorophosphate.

Invention 2 further resides in nonaqueous-electrolyte secondary battery2 which is a nonaqueous-electrolyte secondary battery comprising anegative electrode and a positive electrode which are capable ofoccluding/releasing lithium ions and a nonaqueous electrolyte, whereinthe nonaqueous electrolyte is the nonaqueous electrolyte describedabove.

<Nonaqueous Electrolyte 3 and Nonaqueous-Electrolyte Secondary Battery3>

The inventors diligently made investigations in view of the problemsdescribed above. As a result, they have found that gas evolutioninhibition during continuous charge and battery characteristics can bekept satisfactory when at least one compound selected from the groupconsisting of compounds represented by general formula (1), nitrilecompounds, isocyanate compounds, phosphazene compounds, disulfonic acidester compounds, sulfide compounds, disulfide compounds, acidanhydrides, lactone compounds having a substituent in the α-position,and compounds having a carbon-carbon triple bond is further added to anonaqueous electrolyte containing a monofluorophosphate and/or adifluorophosphate. Invention 3 has been thus completed.

Namely, invention 3 provides nonaqueous electrolyte 3 which is anonaqueous electrolyte mainly comprising an electrolyte and a nonaqueoussolvent dissolving the electrolyte, and the nonaqueous electrolytecomprises: a monofluorophosphate and/or a difluorophosphate; and furtherat least one compound selected from the group consisting of compoundsrepresented by the following general formula (1), nitrile compounds,isocyanate compounds, phosphazene compounds, disulfonic acid estercompounds, sulfide compounds, disulfide compounds, acid anhydrides,lactone compounds having a substituent in the α-position, and compoundshaving a carbon-carbon triple bond (the compound is hereinaftersometimes referred to as “compound A of the invention”):

[wherein R¹, R², and R³ each independently represent a fluorine atom, analkyl group which has 1-12 carbon atoms and may be substituted with afluorine atom, or an alkoxy group which has 1-12 carbon atoms and may besubstituted with a fluorine atom].

Invention 3 further provides nonaqueous-electrolyte secondary battery 3which is a nonaqueous-electrolyte secondary battery at least comprisinga negative electrode and a positive electrode which are capable ofoccluding and releasing lithium ions and a nonaqueous electrolyte,wherein the nonaqueous electrolyte is the nonaqueous electrolytedescribed above.

<Nonaqueous Electrolyte 4 and Nonaqueous-Electrolyte Secondary Battery4>

The inventors diligently made investigations in order to eliminate theproblems described above. As a result, they have found thathigh-current-density charge/discharge characteristics can be inhibitedfrom decreasing and high battery performance can be reconciled with highsafety by using a compound having a coefficient of viscosity not higherthan a certain upper limit together with a cyclic sulfone compound as amain solvent in a nonaqueous electrolyte and by further incorporating aspecific compound. Invention 4 has been thus completed.

Namely, invention 4 resides in nonaqueous electrolyte 4 which is anonaqueous electrolyte comprising an electrolyte and a nonaqueoussolvent dissolving the electrolyte, the nonaqueous electrolytecomprising: a cyclic sulfone compound in an amount of 10-70% by volumebased on the whole nonaqueous solvent; a compound having a coefficientof viscosity at 25° C. of 1.5 mPa·s or lower; and further at least onecompound selected from the group consisting of carbonates having anunsaturated bond, carbonates having a halogen atom,monofluorophosphates, and difluorophosphates.

Invention 4 further resides in nonaqueous-electrolyte secondary battery4 which is a nonaqueous-electrolyte secondary battery comprising anegative electrode and a positive electrode which are capable ofoccluding/releasing lithium ions and a nonaqueous electrolyte, whereinthe nonaqueous electrolyte is the nonaqueous electrolyte describedabove.

<Nonaqueous Electrolyte 5 and Nonaqueous-Electrolyte Secondary Battery5>

The inventors diligently made investigations in order to eliminate theproblems described above. As a result, they have found thathigh-temperature continuous-charge characteristics are greatly improvedwhile maintaining high capacity, by incorporating a cyclic polyaminecompound and/or a cyclic polyamide compound into a nonaqueouselectrolyte and optionally further adding a specific compound, e.g., anunsaturated carbonate. Invention 5 has been thus completed.

Namely, invention 5 resides in nonaqueous electrolyte 5 which is anonaqueous electrolyte comprising a lithium salt and a nonaqueousorganic solvent dissolving the lithium salt, wherein the nonaqueousorganic solvent comprises: a cyclic polyamine compound and/or a cyclicpolyamide compound; and further at least one compound selected from thegroup consisting of unsaturated carbonates, fluorine-containingcarbonates, monofluorophosphates, and difluorophosphates. Hereinafter,this invention is referred to as “embodiment 5-1”.

Invention 5 further resides in a nonaqueous electrolyte which comprisesa lithium salt and a nonaqueous organic solvent dissolving the lithiumsalt, wherein the nonaqueous organic solvent comprises: a cyclicpolyamine compound; and further a cyclic carbonate in an amount of from5% by mass to 40% by mass based on the whole nonaqueous organic solvent.Hereinafter, this invention is referred to as “embodiment 5-2”.

Invention 5 further resides in a nonaqueous electrolyte which comprisesa lithium salt and a nonaqueous organic solvent dissolving the lithiumsalt, wherein the nonaqueous organic solvent comprises a cyclicpolyamide compound. Hereinafter, this invention is referred to as“embodiment 5-3”.

Invention 5 still further resides in nonaqueous-electrolyte secondarybattery 5 characterized by employing any of the nonaqueous electrolytesdescribed above.

<Nonaqueous Electrolyte 6 and Nonaqueous-Electrolyte Secondary Battery6>

The inventors diligently made investigations in view of the problemsdescribed above. As a result, they have found that a nonaqueouselectrolyte to which a specific disulfonylimide salt and a specificcompound have been added can have excellent discharge loadcharacteristics and retain satisfactory high-temperature storability andsatisfactory cycle characteristics. Invention 6 has been thus completed.

Namely, invention 6 resides in nonaqueous electrolyte 6 which is anonaqueous electrolyte mainly comprising an electrolyte and a nonaqueoussolvent dissolving the electrolyte, the nonaqueous electrolytecomprising: at least one cyclic disulfonylimide salt represented by thefollowing general formula (2); and further a monofluorophosphate and/ora difluorophosphate:

[wherein R represents an alkylene group which has 1-12 carbon atoms andmay be substituted with an alkyl group, and the alkyl group and thealkylene group may be substituted with a fluorine atom; n is an integerof 1 to 3; and M is one or more metals selected from Group 1, Group 2,and Group 13 of the periodic table or a quaternary onium].

Invention 6 further resides in nonaqueous-electrolyte secondary battery6 which is a nonaqueous-electrolyte secondary battery comprising anegative electrode and a positive electrode which are capable ofoccluding/releasing lithium ions and a nonaqueous electrolyte, whereinthe nonaqueous electrolyte is the nonaqueous electrolyte describedabove.

Advantages of the Invention

<Nonaqueous Electrolyte 1 and Nonaqueous-Electrolyte Secondary Battery1>

According to invention 1, nonaqueous electrolyte 1 for secondarybatteries and nonaqueous-electrolyte secondary battery 1 can beprovided, which are excellent in discharge load characteristics,high-temperature storability, and cycle characteristics.

<Nonaqueous Electrolyte 2 and Nonaqueous-Electrolyte Secondary Battery2>

According to invention 2, nonaqueous electrolyte 2 andnonaqueous-electrolyte secondary battery 2 can be provided, which haveexcellent discharge load characteristics and are excellent inhigh-temperature storability and cycle characteristics.

<Nonaqueous Electrolyte 3 and Nonaqueous-Electrolyte Secondary Battery3>

According to invention 3, nonaqueous electrolyte 3 andnonaqueous-electrolyte secondary battery 3 can be provided, which areexcellent in cycle characteristics, storability, gas evolutioninhibition during continuous charge, and battery characteristics.

<Nonaqueous Electrolyte 4 and Nonaqueous-Electrolyte Secondary Battery4>

In invention 4, the solvent to be mixed with a cyclic sulfone compoundhas a coefficient of viscosity as low as 1.5 mPa·s or below and thenonaqueous electrolyte as a whole has a lower coefficient of viscositythan that according to patent document 6. High-current-densitycharge/discharge capacity can hence be prevented from decreasing.Namely, according to invention 4, nonaqueous-electrolyte battery 4 canbe provided, which compares ordinary electrolytes in high capacity,high-current-density charge/discharge characteristics, and storabilityand has far higher safety than the general electrolytes. Consequently,not only size increase and performance advancement but also highersafety can be attained in nonaqueous-electrolyte batteries.

<Nonaqueous Electrolyte 5 and Nonaqueous-Electrolyte Secondary Battery5>

According to invention 5, nonaqueous-electrolyte secondary battery 5 canbe provided, which retains a high capacity and is excellent incontinuous-charge characteristics, etc.

<Nonaqueous Electrolyte 6 and Nonaqueous-Electrolyte Secondary Battery6>

According to invention 6, nonaqueous electrolyte 6 for secondarybatteries and nonaqueous-electrolyte secondary battery 6 can beprovided, which have excellent discharge load characteristics and areexcellent also in high-temperature storability and cyclecharacteristics.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be explained below in detail. Thefollowing explanations on constituent elements are for embodiments(typical embodiments) of the invention, and the invention should not beconstrued as being limited to the contents thereof. Variousmodifications of the invention can be made within the spirit of theinvention.

<Nonaqueous Electrolyte 1 and Nonaqueous-Electrolyte Secondary Battery1>

[1. Nonaqueous Electrolyte 1 for Secondary Battery]

Nonaqueous electrolyte 1 of the invention includes an electrolyte and anonaqueous solvent which contains the electrolyte dissolved therein,like ordinary electrolytes.

<1-1. Electrolyte>

The electrolyte to be used in nonaqueous electrolyte 1 of the inventionis not limited, and known ones for use as electrolytes in a targetnonaqueous-electrolyte secondary battery can be employed and mixed atwill. In the case where nonaqueous electrolyte 1 of the invention is tobe used in nonaqueous-electrolyte secondary battery 1, the electrolytepreferably is one or more lithium salts.

Examples of the electrolyte include

inorganic lithium salts such as LiClO₄, LiAsF₆, LiPF₆, Li₂ CO₃, andLiBF₄;

fluorine-containing organic lithium salts such as LiCF₃SO₃,LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, LiN(CF₃SO₂) (C₄F₉SO₂), LiC(CF₃SO₂)₃, LiPF₄(CF₃)₂, LiPF₄ (C₂F₅)₂, LiPF₄ (CF₃SO₂)₂, LiPF₄ (C₂F₅SO₂)₂, LiBF₃ (CF₃),LiBF₃ (C₂F₅), LiBF₂ (CF₃)₂/LiBF₂ (C₂F₅)₂, LiBF₂ (CF₃SO₂)₂, and LiBF₂(C₂F₅SO₂)₂;dicarboxylic-containing acid complex lithium salts such as lithiumbis(oxalato)borate, lithium tris(oxalato)phosphate, and lithiumdifluorooxalatoborate; andsodium salts or potassium salts such as KPF₆, NaPF₆, NaBF₄, and CF₃SO₃Naand the like.

Preferred of these is LiPF₆, LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂,LiN(C₂F₅SO₂)₂, or lithium bis(oxalato)borate. Especially preferred isLiPF₆ or LiBF₄.

One electrolyte may be used alone, or any desired combination of two ormore electrolytes may be used in any desired proportion. In particular,a combination of two specific inorganic lithium salts or a combinationof an inorganic lithium salt and a fluorine-containing organic lithiumsalt is preferred because use of this combination is effective ininhibiting gas evolution during continuous charge or inhibitingdeterioration through high-temperature storage.

It is especially preferred to use a combination of LiPF₆ and LiBF₄ or acombination of an inorganic lithium salt, e.g., LiPF₆ or LiBF₄, and afluorine-containing organic lithium salt, e.g., LiCF₃SO₃, LiN(CF₃SO₂)₂,or LiN(C₂F₅SO₂)₂.

In the case where LiPF₆ and LiBF₄ are used in combination, it ispreferred that the proportion of the LiBF₄ contained should be generally0.01% by mass or higher and generally 20% by mass or lower based on allelectrolytes. LiBF₄ has a low degree of dissociation, and too highproportions thereof may result in cases where nonaqueous electrolyte 1has increased resistance.

On the other hand, in the case where an inorganic lithium salt, e.g.,LiPF₆ or LiBF₄, and a fluorine-containing organic lithium salt, e.g.,LiCF₃SO₃, LiN(CF₃SO₂)₂, or LiN(C₂F₅SO₂)₂, are used in combination, it isdesirable that the proportion of the inorganic lithium salt in alllithium salts should be in the range of from generally 70% by mass togenerally 99% by mass. Since fluorine-containing organic lithium saltsgenerally have a higher molecular weight than inorganic lithium salts,too high proportions of the organic lithium salt in that combinationresults in a reduced proportion of the nonaqueous solvent in the wholenonaqueous electrolyte 1. There are hence cases where nonaqueouselectrolyte 1 has increased resistance.

The lithium salt concentration in the final composition of nonaqueouselectrolyte 1 of the invention may be any desired value unless thisconcentration value considerably lessens the effect of the invention.However, the lithium salt concentration therein is generally 0.5 mol/Lor higher, preferably 0.6 mol/L or higher, more preferably 0.8 mol/L orhigher, and is generally 3 mol/L or lower, preferably 2 mol/L or lower,more preferably 1.5 mol/L or lower. When the concentration thereof istoo low, there are cases where nonaqueous electrolyte 1 has insufficientelectrical conductivity. When the concentration thereof is too high, aviscosity increase occurs and this reduces electrical conductivity.There are hence cases where the nonaqueous-electrolyte secondary batteryemploying this nonaqueous electrolyte 1 of the invention has reducedperformance.

Especially in the case where the nonaqueous solvent of nonaqueouselectrolyte 1 consists mainly of one or more carbonate compounds such asalkylene carbonates or dialkyl carbonates, use of LiPF₆ in combinationwith LiBF₄ is preferred although LiPF₆ may be used alone. This isbecause use of that combination inhibits capacity from deterioratingwith continuous charge. When these two salts are used in combination,the molar ratio of LiBF₄ to LiPF₆ is generally 0.005 or higher,preferably 0.01 or higher, especially preferably 0.05 or higher, and isgenerally 0.4 or lower, preferably 0.2 or lower. In case where the molarratio thereof is too high, battery characteristics tend to decreasethrough high-temperature storage. Conversely, too low molar ratiosthereof result in difficulties in obtaining the effect of inhibiting gasevolution during continuous charge or inhibiting capacity deterioration.

In the case where the nonaqueous solvent of nonaqueous electrolyte 1includes at least 50% by volume cyclic carboxylic ester compound suchas, e.g., γ-butyrolactone or γ-valerolactone, it is preferred that LiBF₄should account for 50 mol % or more of all electrolytes.

<1-2. Carbonate Having Halogen Atom>

The “carbonate having a halogen atom” in invention 1 is not particularlylimited so long as the carbonate has a halogen atom, and any desiredsuch carbonate can be used. Preferred examples the “carbonate having ahalogen atom” include cyclic carbonates having a halogen atom or acycliccarbonates having a halogen atom.

Examples of the halogen atoms include fluorine, chlorine, bromine, andiodine atoms. More preferred of these are fluorine atoms or chlorineatoms. Especially preferred are fluorine atoms. The number of halogenatoms possessed by the “carbonate having a halogen atom” per molecule isnot particularly limited so long as the number thereof is 1 or larger.However, the number thereof is generally 10 or smaller, preferably 6 orsmaller. In the case where the “carbonate having a halogen atom” has twoor more halogen atoms per molecule, these atoms may be the same ordifferent.

<1-2-1. Cyclic Carbonate>

The cyclic carbonate to be used as the “carbonate having a halogen atom”in invention 1 is explained below. The number of the atoms constitutingthe ring of the cyclic carbonate is generally 4 or larger, preferably 5or larger, and the upper limit thereof is preferably 10 or smaller,especially preferably 8 or smaller. When the number thereof is outsidethe range, there are cases where this compound poses a problemconcerning the chemical stability or industrial availability thereof.Examples of such cyclic carbonates in which the numbers ofring-constituting atoms are from 5 to 8 include ethylene carbonate,1,3-propanediol carbonate, 1,4-butanediol carbonate, and 1,5-pentanediolcarbonate, respectively. The cyclic carbonate may have a carbon-carbonunsaturated bond in the ring. Examples thereof include vinylenecarbonate and cis-2-butene-1,4-diol carbonate and the like.

The cyclic carbonate may have one or more substituents each constitutedof a hydrocarbon group. This hydrocarbon group is not limited in thekind thereof, and may be an aliphatic hydrocarbon group or an aromatichydrocarbon group or may be a hydrocarbon group including these twokinds of groups bonded to each other. In the case of an aliphatichydrocarbon group, this group may be an acyclic or cyclic group or maybe a structure including an acyclic moiety and a cyclic moiety bondedthereto. In the case of an acyclic hydrocarbon group, this group may belinear or branched. The hydrocarbon group may be a saturated hydrocarbongroup or may have an unsaturated bond.

Examples of the hydrocarbon group include alkyl groups, cycloalkylgroups, and hydrocarbon groups having an unsaturated bond (hereinaftersuitably referred to as “unsaturated hydrocarbon groups”).

Examples of the alkyl groups include

methyl, ethyl, 1-propyl, 1-methylethyl, 1-butyl, 1-methylpropyl,2-methylpropyl, and 1,1-dimethylethyl.

Preferred of these is methyl or ethyl and the like.

Examples of the cycloalkyl groups include

cyclopentyl, 2-methylcyclopentyl, 3-methylcyclopentyl,2,2-dimethylcyclopentyl, 2,3-dimethylcyclopentyl,2,4-dimethylcyclopentyl, 2,5-dimethylcyclopentyl,3,3-dimethylcyclopentyl, 3,4-dimethylcyclopentyl, 2-ethylcyclopentyl,3-ethylcyclopentyl, cyclohexyl, 2-methylcyclohexyl, 3-methylcyclohexyl,4-methylcyclohexyl, 2,2-dimethylcyclohexyl, 2,3-dimethylcyclohexyl,2,4-dimethylcyclohexyl, 2,5-dimethylcyclohexyl, 2,6-dimethylcyclohexyl,3,4-dimethylcyclohexyl, 3,5-dimethylcyclohexyl, 2-ethylcyclohexyl,3-ethylcyclohexyl, 4-ethylcyclohexyl, bicyclo[3.2.1]oct-1-yl, andbicyclo[3.2.1]oct-2-yl and the like.

Preferred of these is cyclopentyl or cyclohexyl.

Examples of the unsaturated hydrocarbon groups include

vinyl, 1-propen-1-yl, 1-propen-2-yl, allyl, crotyl, ethynyl, propargyl,phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl,2,3-dimethylphenyl, xylyl, phenylmethyl, 1-phenylethyl, 2-phenylethyl,diphenylmethyl, triphenylmethyl, and cinnamyl and the like.

Preferred of these is vinyl, allyl, phenyl, phenylmethyl, or2-phenylethyl.

The hydrocarbon group may be substituted with one or more substituents.The kinds of the substituents are not limited unless the substituentsconsiderably lessen the effects of invention 1. Examples of thesubstituents include hydroxyl groups, amino groups, nitro groups, cyanogroups, carboxyl groups, ether groups, and aldehyde groups. Thehydrocarbon group may have been bonded to the cyclic carbonate throughan oxygen atom. In the case where the hydrocarbon group has two or moresubstituents, these substituents may be the same or different.

When any two or more of such hydrocarbon groups are compared, thehydrocarbon groups may be the same or different. When such hydrocarbongroups have a substituent, these substituted hydrocarbon groupsincluding the substituents may be the same or different. Furthermore,any desired two or more of such hydrocarbon groups may be bonded to eachother to form a cyclic structure.

The number of carbon atoms of the hydrocarbon group is generally 1 orlarger and is generally 20 or smaller, preferably 10 or smaller, morepreferably 6 or smaller. When the number of carbon atoms of thehydrocarbon group is too large, the number of moles per unit weight istoo small and there are cases where various effects are reduced. In thecase where the hydrocarbon group has substituents, the number of carbonatoms of the substituted hydrocarbon group including these substituentsis generally within that range.

The cyclic carbonate having a halogen atom may be one which has halogenatoms directly bonded to carbon atoms constituting the cyclic structureor may be one which has halogen atoms bonded to the “substituentconstituted of a hydrocarbon group” described above. Alternatively, thecyclic carbonate may be one which has halogen atoms respectively bondedto both of those.

In the case where the structure composed of the “substituent constitutedof a hydrocarbon group” and a halogen atom bonded thereto is ahalogenated alkyl group, examples thereof include

monofluoromethyl, difluoromethyl, trifluoromethyl, 1-fluoroethyl,2-fluoroethyl, 1,1-difluoroethyl, 1,2-difluoroethyl, 2,2-difluoroethyl,2,2,2-trifluoroethyl, perfluoroethyl, monochloromethyl, dichloromethyl,trichloromethyl, 1-chloroethyl, 2-chloroethyl, 1,1-dichloroethyl,1,2-dichloroethyl, 2,2-dichloroethyl, 2,2,2-trichloroethyl, andperchloroethyl and the like.

Preferred of these is monofluoromethyl, difluoromethyl, trifluoromethyl,2,2-difluoroethyl, 2,2,2-trifluoroethyl, or perfluoroethyl.

In the case where the structure composed of the “substituent constitutedof a hydrocarbon group” and a halogen atom bonded thereto is ahalogenated cycloalkyl group, examples thereof include

1-fluorocyclopentyl, 2-fluorocyclopentyl, 3-fluorocyclopentyl,difluorocyclopentyl, trifluorocyclopentyl, 1-fluorocyclohexyl,2-fluorocyclohexyl, 3-fluorocyclohexyl, 4-fluorocyclohexyl,difluorocyclohexyl, trifluorocyclohexyl, 1-chlorocyclopentyl,2-chlorocyclopentyl, 3-chlorocyclopentyl, dichlorocyclopentyl,trichlorocyclopentyl, 1-chlorocyclohexyl, 2-chlorocyclohexyl,3-chlorocyclohexyl, 4-chlorocyclohexyl, dichlorocyclohexyl, andtrichlorocyclohexyl and the like.

Preferred of these is 1-fluorocyclopentyl, 2-fluorocyclopentyl,3-fluorocyclopentyl, 1-fluorocyclohexyl, 2-fluorocyclohexyl,3-fluorocyclohexyl, or 4-fluorocyclohexyl.

In the case where the structure composed of the “substituent constitutedof a hydrocarbon group” and a halogen atom bonded thereto is ahalogenated unsaturated hydrocarbon group, examples thereof include

1-fluorovinyl, 2-fluorovinyl, 1,2-difluorovinyl, perfluorovinyl,1-fluoroallyl, 2-fluoroallyl, 3-fluoroallyl, 2-fluorophenyl,3-fluorophenyl, 4-fluorophenyl, 2,3-difluorophenyl, 2,4-difluorophenyl,2,5-difluorophenyl, 2,6-difluorophenyl, 3,4-difluorophenyl,3,5-difluorophenyl, 1-fluoro-1-phenylmethyl,1,1-difluoro-1-phenylmethyl, (2-fluorophenyl)methyl,(3-fluorophenyl)methyl, (4-fluorophenyl)methyl,(2-fluorophenyl)fluoromethyl, 1-fluoro-2-phenylethyl,1,1-difluoro-2-phenylethyl, 1,2-difluoro-2-phenylethyl,2-(2-fluorophenyl)ethyl, 2-(3-fluorophenyl)ethyl,2-(4-fluorophenyl)ethyl, 1-fluoro-2-(2-fluorophenyl)ethyl,1-fluoro-2-(2-fluorophenyl)ethyl,1-chlorovinyl, 2-chlorovinyl, 1,2-dichlorovinyl, perchlorovinyl,1-chloroallyl, 2-chloroallyl, 3-chloroallyl, 2-chlorophenyl,3-chlorophenyl, 4-chlorophenyl, 2,3-dichlorophenyl, 2,4-dichlorophenyl,2,5-dichlorophenyl, 2,6-dichlorophenyl, 3,4-dichlorophenyl,1,5-dichlorophenyl, 1-chloro-1-phenylmethyl,1,1-dichloro-1-phenylmethyl, (2-chlorophenyl)methyl,(3-chlorophenyl)methyl, (4-chlorophenyl)methyl,(2-chlorophenyl)chloromethyl, 1-chloro-2-phenylethyl,1,1-dichloro-2-phenylethyl, 1,2-dichloro-2-phenylethyl,2-(2-chlorophenyl)ethyl, 2-(3-chlorophenyl)ethyl,2-(4-chlorophenyl)ethyl, 1-chloro-2-(2-chlorophenyl)ethyl, and1-chloro-2-(2-chlorophenyl)ethyl and the like.

Preferred of these is 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl,2,4-difluorophenyl, 3,5-difluorophenyl, 1-fluoro-1-phenylmethyl,(2-fluorophenyl)methyl, (4-fluorophenyl)methyl,(2-fluorophenyl)fluoromethyl, 1-fluoro-2-phenylethyl,2-(2-fluorophenyl)ethyl, or 2-(4-fluorophenyl)ethyl.

Specific examples of such cyclic carbonates having a halogen atominclude

fluoroethylene carbonate, chloroethylene carbonate, 4,4-difluoroethylenecarbonate, 4,5-difluoroethylene carbonate, 4,4-dichloroethylenecarbonate, 4,5-dichloroethylene carbonate, 4-fluoro-4-methylethylenecarbonate, 4-chloro-4-methylethylene carbonate,4-fluoro-5-methylethylene carbonate, 4-chloro-5-methylethylenecarbonate, 4,5-difluoro-4-methylethylene carbonate,4,5-dichloro-4-methylethylene carbonate, 4-fluoro-5-methylethylenecarbonate, 4-chloro-5-methylethylene carbonate,4,4-difluoro-5-methylethylene carbonate, 4,4-dichloro-5-methylethylenecarbonate, 4-(fluoromethyl)ethylene carbonate, 4-(chloromethyl)ethylenecarbonate, 4-(difluoromethyl)ethylene carbonate,4-(dichloromethyl)ethylene carbonate, 4-(trifluoromethyl)ethylenecarbonate, 4-(trichloromethyl)ethylene carbonate,4-(fluoromethyl)-4-fluoroethylene carbonate,4-(chloromethyl)-4-chloroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-(chloromethyl)-5-chloroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate, 4-chloro-4,5-dimethylethylenecarbonate, 4,5-difluoro-4,5-dimethylethylene carbonate,4,5-dichloro-4,5-dimethylethylene carbonate,4,4-difluoro-5,5-dimethylethylene carbonate, and4,4-dichloro-5,5-dimethylethylene carbonate and the like.

Examples of the “cyclic carbonate having a halogen atom” which has acarbon-carbon unsaturated bond in the ring include

fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate,4-fluoro-5-phenylvinylene carbonate, 4-(trifluoromethyl)vinylenecarbonate, chlorovinylene carbonate, 4-chloro-5-methylvinylenecarbonate, 4-chloro-5-phenylvinylene carbonate, and4-(trichloromethyl)vinylene carbonate and the like.

Examples of the cyclic carbonate substituted with one or morehydrocarbon groups and having one or more carbon-carbon unsaturatedbonds outside the ring include

4-fluoro-4-vinylethylene carbonate, 4-fluoro-5-vinylethylene carbonate,4,4-difluoro-5-vinylethylene carbonate, 4,5-difluoro-4-vinylethylenecarbonate, 4-chloro-5-vinylethylene carbonate,4,4-dichloro-5-vinylethylene carbonate, 4,5-dichloro-4-vinylethylenecarbonate, 4-fluoro-4,5-divinylethylene carbonate,4,5-difluoro-4,5-divinylethylene carbonate, 4-chloro-4,5-divinylethylenecarbonate, 4,5-dichloro-4,5-divinylethylene carbonate,4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylenecarbonate, 4,4-difluoro-5-phenylethylene carbonate,4,5-difluoro-4-phenylethylene carbonate, 4-chloro-4-phenylethylenecarbonate, 4-chloro-5-phenylethylene carbonate,4,4-dichloro-5-phenylethylene carbonate, 4,5-dichloro-4-phenylethylenecarbonate, 4,5-difluoro-4,5-diphenylethylene carbonate,4,5-dichloro-4,5-diphenylethylene carbonate, 4-fluoro-5-vinylvinylenecarbonate and, 4-chloro-5-vinylvinylene carbonate and the like.

Preferred of those cyclic carbonates having a halogen atom are thecarbonates having a fluorine atom. In particular, fluoroethylenecarbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylenecarbonate, 4-fluoro-4-methylethylene carbonate,4-fluoro-5-methylethylene carbonate, 4-(fluoromethyl)-ethylenecarbonate, or 4-(trifluoromethyl)-ethylene carbonate is more preferredfrom the standpoints of industrial availability and chemical stability.

The molecular weight of the cyclic carbonate having a halogen atom isnot particularly limited, and may be any value unless the effects ofinvention 1 are considerably lessened thereby. However, the molecularweight thereof is generally 50 or higher, preferably 80 or higher, andis generally 250 or lower, preferably 150 or lower. When the cycliccarbonate has too high a molecular weight, this cyclic carbonate havinga halogen atom has reduced solubility in nonaqueous electrolyte 1 andthere are cases where it is difficult to sufficiently produce theeffects of invention 1.

Processes for producing the cyclic carbonate having a halogen atom alsoare not particularly limited. The cyclic carbonate can be produced by aknown process selected at will.

Any one of those cyclic carbonates having a halogen atom explained abovemay be contained alone in nonaqueous electrolyte 1 of the invention, orany desired combination of two or more of these may be contained in anydesired proportion. The content of the cyclic carbonate(s) having ahalogen atom is not particularly limited. However, the content thereofis generally from 0.001% by mass to 100% by mass.

It is thought that the cyclic carbonate having a halogen atom performsdifferent functions according to the content thereof. Factors in thishave not been elucidated in detail. Although the scope of invention 1should not be construed as being limited by the factors, the followingis thought. In the case where the cyclic carbonate having a halogen atomis used as an additive in an amount of from 0.001% by mass to 10% bymass based on the whole nonaqueous solvent, this cyclic carbonate isthought to decompose on the surface of the negative electrode to form aprotective film for protecting the surface of the negative electrode. Onthe other hand, in the case where the cyclic carbonate having a halogenatom is used as a nonaqueous solvent in an amount of from 10% by mass to100% by mass, this cyclic carbonate is thought to not only perform thatfunction of an additive but also perform the function of improving theoxidation resistance of nonaqueous electrolyte 1.

In the case where the cyclic carbonate having a halogen atom is used asan additive, the content thereof is generally 0.001% by mass or higher,preferably 0.01% by mass or higher, and is generally 10% by mass orlower, preferably 5% by mass or lower, based on the whole nonaqueoussolvent. When the content thereof is too low, there are cases where theformation of a negative-electrode coating film based on the reductionaldecomposition of the cyclic carbonate is insufficient, making itimpossible to impart sufficient battery characteristics.

In the case where the cyclic carbonate having a halogen atom is used asa nonaqueous solvent, the content thereof is generally 10% by mass orhigher, preferably 12% by mass or higher, most preferably 15% by mass orhigher, and is generally 100% by mass or lower, preferably 80% by massor lower, most preferably 50% by mass or lower, based on the wholenonaqueous solvent. When the content thereof is lower than the lowerlimit, there are cases where the oxidative decomposition of othercomponents of nonaqueous electrolyte 1 which proceeds on the surface ofthe positive electrode is not inhibited to a desirable degree, making itimpossible to produce the effects of invention 1. On the other hand,contents thereof higher than the upper limit result in an increasedviscosity of the electrolyte and there are hence cases where theincreased viscosity reduces various characteristics of the battery.

The cyclic carbonate having a halogen atom may be used as a mixture withthe acyclic carbonate having a halogen atom which will be describedlater and/or the “nonaqueous solvent other than the carbonates having ahalogen atom” which will be described later, in any desired proportion.Examples of combinations in the case of employing such a mixtureinclude:

a cyclic carbonate having a halogen atom and a cyclic carbonate havingno halogen atoms; a cyclic carbonate having a halogen atom and anacyclic carbonate having no halogen atoms; a cyclic carbonate having ahalogen atom and an acyclic carbonate having a halogen atom; a cycliccarbonate having a halogen atom and a cyclic carboxylic acid ester; acyclic carbonate having a halogen atom and an acyclic carboxylic acidester; a cyclic carbonate having a halogen atom and a cyclic ether; acyclic carbonate having a halogen atom and an acyclic ether; a cycliccarbonate having a halogen atom and a phosphorus-containing organicsolvent; a cyclic carbonate having a halogen atom, a cyclic carbonatehaving no halogen atoms, and an acyclic carbonate having no halogenatoms; a cyclic carbonate having a halogen atom, a cyclic carbonatehaving no halogen atoms, and an acyclic carbonate having a halogen atom;a cyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, and a cyclic carboxylic acid ester; a cyclic carbonatehaving a halogen atom, a cyclic carbonate having no halogen atoms, andan acyclic carboxylic acid ester; a cyclic carbonate having a halogenatom, a cyclic carbonate having no halogen atoms, and a cyclic ether; acyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, and an acyclic ether; a cyclic carbonate having a halogenatom, a cyclic carbonate having no halogen atoms, an acyclic carbonatehaving no halogen atoms, and an acyclic carbonate having a halogen atom;a cyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, a cyclic carboxylic acid ester, and an acyclic carbonatehaving no halogen atoms; a cyclic carbonate having a halogen atom, acyclic carbonate having no halogen atoms, an acyclic carboxylic acidester, and an acyclic carbonate having no halogen atoms; a cycliccarbonate having a halogen atom, a cyclic carbonate having no halogenatoms, a cyclic ether, and an acyclic carbonate having no halogen atoms;a cyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, an acyclic ether, and an acyclic carbonate having nohalogen atoms;a cyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, a phosphorus-containing organic solvent, and an acycliccarbonate having no halogen atoms;a cyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, a cyclic carboxylic acid ester, and an acyclic carbonatehaving a halogen atom; a cyclic carbonate having a halogen atom, acyclic carbonate having no halogen atoms, a cyclic carboxylic acidester, and an acyclic carbonate having no halogen atoms; a cycliccarbonate having a halogen atom, a cyclic carbonate having no halogenatoms, a cyclic carboxylic acid ester, and an acyclic carboxylic acidester; a cyclic carbonate having a halogen atom, a cyclic carbonatehaving no halogen atoms, a cyclic carboxylic acid ester, and a cyclicether; a cyclic carbonate having a halogen atom, a cyclic carbonatehaving no halogen atoms, a cyclic carboxylic acid ester, and aphosphorus-containing organic solvent;a cyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, a cyclic carboxylic acid ester, an acyclic carbonatehaving a halogen atom, and an acyclic carbonate having no halogen atoms;a cyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, a cyclic ether, an acyclic carbonate having a halogenatom, and an acyclic carbonate having no halogen atoms; and a cycliccarbonate having a halogen atom, a cyclic carbonate having no halogenatoms, a phosphorus-containing organic solvent, an acyclic carbonatehaving a halogen atom, and an acyclic carbonate having no halogen atomsand the like.<1-2-2. Acyclic Carbonate>

The acyclic carbonate to be used as the “carbonate having a halogenatom” in invention 1 is explained below. The acyclic carbonate usuallyhas two hydrocarbon groups, and these hydrocarbon groups may be the sameor different. The number of carbon atoms of each of these hydrocarbongroups is preferably 1 or larger, and the upper limit thereof ispreferably 10 or smaller, especially preferably 6 or smaller. When thenumber thereof is outside the range, there are cases where this compoundposes a problem concerning the chemical stability and industrialavailability thereof.

Examples of the hydrocarbon groups constituting such an acycliccarbonate include ones which are the same as the substituents with whichthe cyclic carbonate may be substituted, and further include hydrocarbongroups which are the same as the halogenated substituents.

Examples of the acyclic carbonate include

dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutylcarbonate, divinyl carbonate, diallyl carbonate, diphenyl carbonate,ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate,methyl vinyl carbonate, allyl methyl carbonate, methyl phenyl carbonate,ethyl propyl carbonate, butyl ethyl carbonate, ethyl vinyl carbonate,allyl ethyl carbonate, and ethyl phenyl carbonate and the like.

Preferred of these from the standpoints of industrial availability, etc.are dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylmethyl carbonate, methyl vinyl carbonate, ethyl vinyl carbonate, allylmethyl carbonate, allyl ethyl carbonate, methyl phenyl carbonate, ethylphenyl carbonate, and the like.

Examples of those acyclic carbonates which have been halogenated include

fluoromethyl methyl carbonate, difluoromethyl methyl carbonate,trifluoromethyl methyl carbonate, bis(fluoromethyl)carbonate,bis(difluoro)methyl carbonate, bis(trifluoro)methyl carbonate,chloromethyl methyl carbonate, dichloromethyl methyl carbonate,trichloromethyl methyl carbonate, bis(chloromethyl)carbonate,bis(dichloro)methyl carbonate, bis(trichloro)methyl carbonate,2-fluoroethyl methyl carbonate, ethyl fluoromethyl carbonate,2,2-difluoroethyl methyl carbonate, 2-fluoroethyl fluoromethylcarbonate, ethyl difluoromethyl carbonate, 2,2,2-trifluoroethyl methylcarbonate, 2,2-difluoroethyl fluoromethyl carbonate, 2-fluoroethyldifluoromethyl carbonate, ethyl trifluoromethyl carbonate, 2-chloroethylmethyl carbonate, ethyl chloromethyl carbonate, 2,2-dichloroethyl methylcarbonate, 2-chloroethyl chloromethyl carbonate, ethyl dichloromethylcarbonate, 2,2,2-trichloroethyl methyl carbonate, 2,2-dichloroethylchloromethyl carbonate, 2-chloroethyl dichloromethyl carbonate, ethyltrichloromethyl carbonate,ethyl 2-fluoroethyl carbonate, ethyl 2,2-difluoroethyl carbonate,bis(2-fluoroethyl)carbonate, ethyl 2,2,2-trifluoroethyl carbonate,2,2-difluoroethyl-2′-fluoroethyl carbonate,bis(2,2-difluoroethyl)carbonate, 2,2,2-trifluoroethyl-2′-fluoroethylcarbonate, 2,2,2-trifluoroethyl-2′,2′-difluoroethyl carbonate,bis(2,2,2-trifluoroethyl)carbonate, ethyl 2-chloroethyl carbonate, ethyl2,2-dichloroethyl carbonate, bis(2-chloroethyl)carbonate, ethyl2,2,2-trichloroethyl carbonate, 2,2-dichloroethyl-2′-chloroethylcarbonate, bis(2,2-dichloroethyl)carbonate,2,2,2-trichloroethyl-2′-chloroethyl carbonate,2,2,2-trichloroethyl-2′,2′-dichloroethyl carbonate,bis(2,2,2-trichloroethyl)carbonate,fluoromethyl vinyl carbonate, 2-fluoroethyl vinyl carbonate,2,2-difluoroethyl vinyl carbonate, 2,2,2-trifluoroethyl vinyl carbonate,chloromethyl vinyl carbonate, 2-chloroethyl vinyl carbonate,2,2-dichloroethyl vinyl carbonate, 2,2,2-trichloroethyl vinyl carbonate,fluoromethyl allyl carbonate, 2-fluoroethyl allyl carbonate,2,2-difluoroethyl allyl carbonate, 2,2,2-trifluoroethyl allyl carbonate,chloromethyl allyl carbonate, 2-chloroethyl allyl carbonate,2,2-dichloroethyl allyl carbonate, 2,2,2-trichloroethyl allyl carbonate,fluoromethyl phenyl carbonate, 2-fluoroethyl phenyl carbonate,2,2-difluoroethyl phenyl carbonate, 2,2,2-trifluoroethyl phenylcarbonate, chloromethyl phenyl carbonate, 2-chloroethyl phenylcarbonate, 2,2-dichloroethyl phenyl carbonate, and 2,2,2-trichloroethylphenyl carbonate and the like.

Preferred of these acyclic carbonates having a halogen atom are thecarbonates having a fluorine atom. In particular, the followingcarbonates are more preferred from the standpoints of industrialavailability and chemical stability: fluoromethyl methyl carbonate,bis(fluoromethyl)carbonate, difluoromethyl methyl carbonate,2,2-difluoroethyl methyl carbonate, ethyl 2,2-difluoroethyl carbonate,bis(2,2-difluoroethyl)carbonate, 2,2,2-trifluoroethyl methyl carbonate,ethyl 2,2,2-trifluoroethyl carbonate, andbis(2,2,2-trifluoroethyl)carbonate.

The molecular weight of the acyclic carbonate having a halogen atom isnot particularly limited, and may be any value unless the effects ofinvention 1 are considerably lessened thereby. However, the molecularweight thereof is generally 50 or higher, preferably 80 or higher, andis generally 250 or lower, preferably 150 or lower. When the acycliccarbonate has too high a molecular weight, this acyclic carbonate havinga halogen atom has reduced solubility in nonaqueous electrolyte 1 andthere are cases where it is difficult to sufficiently produce theeffects of invention 1.

Processes for producing the acyclic carbonate having a halogen atom alsoare not particularly limited. The acyclic carbonate can be produced by aknown process selected at will.

Any one of those acyclic carbonates having a halogen atom explainedabove may be contained alone in nonaqueous electrolyte 1 of theinvention, or any desired combination of two or more of these may becontained in any desired proportion.

It is thought that the acyclic carbonate having a halogen atom performsdifferent functions according to the content thereof. Factors in thishave not been elucidated in detail. Although the scope of invention 1should not be construed as being limited by the factors, the followingis thought. In the case where the acyclic carbonate having a halogenatom is used as an additive in an amount of from 0.001% by mass to 10%by mass based on the whole nonaqueous solvent, this acyclic carbonate isthought to decompose on the surface of the negative electrode to form aprotective film for protecting the surface of the negative electrode. Onthe other hand, in the case where the acyclic carbonate having a halogenatom is used as a nonaqueous solvent in an amount of from 10% by mass to100% by mass, this acyclic carbonate is thought to not only perform thatfunction of an additive but also perform the function of improving theoxidation resistance of nonaqueous electrolyte 1.

In the case where the acyclic carbonate having a halogen atom is used asan additive, the content thereof is generally 0.001% by mass or higher,preferably 0.01% by mass or higher, and is generally 10% by mass orlower, preferably 5% by mass or lower, based on the whole nonaqueoussolvent. When the content thereof is too low, there are cases where theformation of a negative-electrode coating film based on the reductionaldecomposition of the acyclic carbonate is insufficient, making itimpossible to impart sufficient battery characteristics.

In the case where the acyclic carbonate having a halogen atom is used asa nonaqueous solvent, the content thereof is generally 10% by mass orhigher, preferably 12% by mass or higher, most preferably 15% by mass orhigher, and is generally 100% by mass or lower, preferably 80% by massor lower, most preferably 50% by mass or lower, based on the wholenonaqueous solvent. When the content thereof is lower than the lowerlimit, there are cases where the oxidative decomposition of othercomponents of nonaqueous electrolyte 1 which proceeds on the surface ofthe positive electrode is not inhibited to a desirable degree, making itimpossible to produce the effects of invention 1. On the other hand,contents thereof higher than the upper limit result in an increasedviscosity of the electrolyte and there are hence cases where theincreased viscosity reduces various characteristics of the battery.

The acyclic carbonate having a halogen atom may be used as a mixturewith the cyclic carbonate having a halogen atom which was describedabove and/or the “nonaqueous solvent other than the carbonates having ahalogen atom” which will be described later, in any desired proportion.Examples of combinations in the case of employing such a mixtureinclude:

an acyclic carbonate having a halogen atom and a cyclic carbonate havingno halogen atoms; an acyclic carbonate having a halogen atom and acyclic carbonate having a halogen atom; an acyclic carbonate having ahalogen atom and a cyclic carboxylic acid ester; an acyclic carbonatehaving a halogen atom and a phosphorus-containing organic solvent;an acyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, and an acyclic carbonate; an acyclic carbonate having ahalogen atom, a cyclic carbonate having no halogen atoms, and a cycliccarbonate having a halogen atom; an acyclic carbonate having a halogenatom, a cyclic carbonate having no halogen atoms, and a cycliccarboxylic acid ester; an acyclic carbonate having a halogen atom, acyclic carbonate having no halogen atoms, and a phosphorus-containingorganic solvent; an acyclic carbonate having a halogen atom, a cycliccarbonate having a halogen atom, and an acyclic carbonate; an acycliccarbonate having a halogen atom, a cyclic carbonate having a halogenatom, and a cyclic carboxylic acid ester; an acyclic carbonate having ahalogen atom, a cyclic carbonate having a halogen atom, and aphosphorus-containing organic solvent; an acyclic carbonate having ahalogen atom, a cyclic carbonate having no halogen atoms, an acycliccarbonate, and a cyclic carboxylic acid ester;an acyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, a cyclic carbonate having a halogen atom, and a cycliccarboxylic acid ester; an acyclic carbonate having a halogen atom, acyclic carbonate having no halogen atoms, a phosphorus-containingorganic solvent, and a cyclic carboxylic acid ester; an acycliccarbonate having a halogen atom, a cyclic carbonate having no halogenatoms, a cyclic carboxylic acid ester, and an acyclic carbonate havingno halogen atoms; an acyclic carbonate having a halogen atom, a cycliccarbonate having no halogen atoms, a cyclic ether, and an acycliccarbonate having no halogen atoms; an acyclic carbonate having a halogenatom, a cyclic carbonate having no halogen atoms, aphosphorus-containing organic solvent, and an acyclic carbonate havingno halogen atoms;an acyclic carbonate having a halogen atom, a cyclic carbonate having nohalogen atoms, a cyclic carbonate having a halogen atom, and an acycliccarbonate having no halogen atoms; an acyclic carbonate having a halogenatom, a cyclic carbonate having no halogen atoms, a cyclic carbonatehaving a halogen atom, and a cyclic carboxylic acid ester; an acycliccarbonate having a halogen atom, a cyclic carbonate having no halogenatoms, a cyclic carbonate having a halogen atom, a cyclic carboxylicacid ester, and an acyclic carbonate having no halogen atoms; an acycliccarbonate having a halogen atom, a cyclic carbonate having no halogenatoms, a cyclic carbonate having a halogen atom, a cyclic ether, and anacyclic carbonate having no halogen atoms; and an acyclic carbonatehaving a halogen atom, a cyclic carbonate having no halogen atoms, acyclic carbonate having a halogen atom, a phosphorus-containing organicsolvent, and an acyclic carbonate having no halogen atoms and the like.<1-3. Nonaqueous Solvent Other than Carbonates Having Halogen Atom>

The “nonaqueous solvent other than carbonates having a halogen atom”which may be contained in nonaqueous electrolyte 1 of the invention isnot particularly limited so long as it is a solvent which, after used tofabricate a battery, exerts no adverse influence on the batterycharacteristics. However, this solvent preferably is one or more of thefollowing “nonaqueous solvents other than carbonates having a halogenatom”.

Examples of the “nonaqueous solvent other than carbonates having ahalogen atom” include acyclic or cyclic carbonates, acyclic or cycliccarboxylic acid esters, acyclic or cyclic ethers, phosphorus-containingorganic solvents, and sulfur-containing organic solvents and the like.

The acyclic carbonates also are not limited in the kind thereof.However, dialkyl carbonates are preferred. The number of carbon atoms ofeach constituent alkyl group is preferably 1-5, especially preferably1-4. Examples thereof include

dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyln-propyl carbonate, ethyl n-propyl carbonate, and di-n-propyl carbonateand the like.

Of these, dimethyl carbonate, ethyl methyl carbonate, or diethylcarbonate is preferred from the standpoint of industrial availabilityand because these compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The cyclic carbonates are not limited in the kind thereof. However, thenumber of carbon atoms of the alkylene group constituting each cycliccarbonate is preferably 2-6, especially preferably 2-4. Examples of thecyclic carbonates include ethylene carbonate, propylene carbonate, andbutylene carbonate (2-ethylethylene carbonate or cis- ortrans-2,3-dimethylethylene carbonate) and the like.

Of these, ethylene carbonate or propylene carbonate is preferred becausethese compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The acyclic carboxylic acid esters also are not limited in the kindthereof. Examples thereof include methyl acetate, ethyl acetate,n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate,tert-butyl acetate, methyl propionate, ethyl propionate, n-propylpropionate, isopropyl propionate, n-butyl propionate, isobutylpropionate, and tert-butyl propionate and the like.

Of these, ethyl acetate, methyl propionate, or ethyl propionate ispreferred from the standpoint of industrial availability and becausethese compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The cyclic carboxylic acid esters also are not limited in the kindthereof. Examples of such esters in ordinary use includeγ-butyrolactone, γ-valerolactone, and δ-valerolactone and the like.

Of these, γ-butyrolactone is preferred from the standpoint of industrialavailability and because this compound is satisfactory in variousproperties in a nonaqueous-electrolyte secondary battery.

The acyclic ethers also are not limited in the kind thereof. Examplesthereof include

dimethoxymethane, dimethoxyethane, diethoxymethane, diethoxyethane,ethoxymethoxymethane, and ethoxymethoxyethane and the like.

Of these, dimethoxyethane or diethoxyethane is preferred from thestandpoint of industrial availability and because these compounds aresatisfactory in various properties in a nonaqueous-electrolyte secondarybattery.

The cyclic ethers also are not limited in the kind thereof. Examples ofsuch ethers in ordinary use include tetrahydrofuran,2-methyltetrahydrofuran, and tetrahydropyran and the like.

The phosphorus-containing organic solvents also are not particularlylimited in the kind thereof. Examples thereof include

phosphoric acid esters such as trimethyl phosphate, triethyl phosphate,and triphenyl phosphate;

phosphorous acid esters such as trimethyl phosphite, triethyl phosphite,and triphenyl phosphite; and

phosphine oxides such as trimethylphosphine oxide, triethylphosphineoxide, and triphenylphosphine oxide and the like.

Furthermore, the sulfur-containing organic solvents also are notparticularly limited in the kind thereof. Examples thereof include

ethylene sulfite, 1,3-propanesultone, 1,4-butanesultone, methylmethanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone,diphenyl sulfone, methyl phenyl sulfone, dibutyl disulfide, dicyclohexyldisulfide, tetramethylthiuram monosulfide,N,N-dimethylmethanesulfonamide, and N,N-diethylmethanesulfonamide andthe like.

Of those compounds, the acyclic or cyclic carbonates or the acyclic orcyclic carboxylic acid esters are preferred because these compounds aresatisfactory in various properties in a nonaqueous-electrolyte secondarybattery. More preferred of these is ethylene carbonate, propylenecarbonate, dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, ethyl acetate, methyl propionate, ethyl propionate, orγ-butyrolactone. Especially preferred is dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethyl acetate, methyl propionate,or ethyl propionate.

Those compounds may be used alone or in combination of two or morethereof. It is, however, preferred to use two or more compounds incombination. For example, it is especially preferred to use ahigh-permittivity solvent, such as a cyclic carbonate, in combinationwith a low-viscosity solvent, such as an acyclic carbonate or an acyclicester and the like.

A preferred combination of “nonaqueous solvents other than carbonateshaving a halogen atom” is a combination consisting mainly of at leastone of cyclic carbonates and at least one of acyclic carbonates. Inparticular, the total proportion of the cyclic carbonate and the acycliccarbonate to the whole nonaqueous solvent is generally 80% by volume orhigher, preferably 85% by volume or higher, more preferably 90% byvolume or higher. The proportion by volume of the cyclic carbonate tothe sum of the cyclic carbonate and the acyclic carbonate is preferably5% by volume or higher, more preferably 10% by volume or higher,especially preferably 15% by volume or higher, and is generally 50% byvolume or lower, preferably 35% by volume or lower, more preferably 30%by volume or lower. Use of such combination of “nonaqueous solventsother than carbonates having a halogen atom” is preferred because thebattery fabricated with this combination has an improved balance betweencycle characteristics and high-temperature storability (in particular,residual capacity and high-load discharge capacity afterhigh-temperature storage).

Examples of the preferred combination including at least one cycliccarbonate and at least one acyclic carbonate include: ethylene carbonateand dimethyl carbonate; ethylene carbonate and diethyl carbonate;ethylene carbonate and ethyl methyl carbonate; ethylene carbonate,dimethyl carbonate, and diethyl carbonate; ethylene carbonate, dimethylcarbonate, and ethyl methyl carbonate; ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate; and ethylene carbonate, dimethylcarbonate, diethyl carbonate, and ethyl methyl carbonate and the like.

Combinations obtained by further adding propylene carbonate to thosecombinations including ethylene carbonate and one or more acycliccarbonates are also included in preferred combinations. In the casewhere propylene carbonate is contained, the volume ratio of the ethylenecarbonate to the propylene carbonate is preferably from 99:1 to 40:60,especially preferably from 95:5 to 50:50. It is also preferred toregulate the proportion of the propylene carbonate to the wholenonaqueous solvent to a value which is 0.1% by volume or higher,preferably 1% by volume or higher, more preferably 2% by volume orhigher, and is generally 10% by volume or lower, preferably 8% by volumeor lower, more preferably 5% by volume or lower. This is because thisregulation brings about excellent discharge load characteristics whilemaintaining the properties of the combination of ethylene carbonate andone or more acyclic carbonates.

More preferred of these are combinations including an asymmetric acycliccarbonate. In particular, combinations including ethylene carbonate, asymmetric acyclic carbonate, and an asymmetric acyclic carbonate, suchas a combination of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate, a combination of ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate, and a combination of ethylenecarbonate, dimethyl carbonate, diethyl carbonate, and ethyl methylcarbonate, or such combinations which further contain propylenecarbonate are preferred because these combinations have a satisfactorybalance between cycle characteristics and discharge loadcharacteristics. Preferred of such combinations are ones in which theasymmetric acyclic carbonate is ethyl methyl carbonate. Furthermore, thenumber of carbon atoms of each of the alkyl groups constituting eachdialkyl carbonate is preferably 1-2.

Other examples of preferred mixed solvents are ones containing anacyclic ester. In particular, the cyclic carbonate/acyclic carbonatemixed solvents which contain an acyclic ester are preferred from thestandpoint of improving the low-temperature characteristics of abattery. The acyclic ester especially preferably is ethyl acetate ormethyl propionate. The proportion by volume of the acyclic ester to thewhole nonaqueous solvent is generally 5% or higher, preferably 8% orhigher, more preferably 15% or higher, and is generally 50% or lower,preferably 35% or lower, more preferably 30% or lower, even morepreferably 25% or lower.

Other preferred examples of the “nonaqueous solvent other thancarbonates having a halogen atom” are ones in which one organic solventselected from the group consisting of ethylene carbonate, propylenecarbonate, butylene carbonate, γ-butyrolactone, and γ-valerolactone or amixed solvent composed of two or more organic solvents selected from thegroup accounts for at least 60% by volume of the whole. Such mixedsolvents have a flash point of preferably 50° C. or higher, especiallypreferably 70° C. or higher. Nonaqueous electrolyte 1 employing thissolvent is reduced in solvent vaporization and liquid leakage even whenused at high temperatures. In particular, when such a nonaqueous solventwhich includes ethylene carbonate and γ-butyrolactone in a total amountof 80% by volume or larger, preferably 90% by volume or larger, based onthe whole nonaqueous solvent and in which the volume ratio of theethylene carbonate to the γ-butyrolactone is from 5:95 to 45:55 or sucha nonaqueous solvent which includes ethylene carbonate and propylenecarbonate in a total amount of 80% by volume or larger, preferably 90%by volume or larger, based on the whole nonaqueous solvent and in whichthe volume ratio of the ethylene carbonate to the propylene carbonate isfrom 30:70 to 80:20 is used, then an improved balance between cyclecharacteristics and discharge load characteristics, etc. is generallyobtained.

<1-3. Monofluorophosphate and Difluorophosphate>

Nonaqueous electrolyte 1 of the invention contains a monofluorophosphateand/or a difluorophosphate as an essential component. The“monofluorophosphate and/or difluorophosphate” to be used in theinvention is not particularly limited in the kind thereof so long asthis ingredient is constituted of one or more monofluorophosphate ionsand/or difluorophosphate ions and one or more cations. However, thisingredient must be selected in view of the necessity of finallyproducing a nonaqueous electrolyte usable as the electrolyte of anonaqueous-electrolyte secondary battery to be used.

It is therefore preferred that the monofluorophosphate and/ordifluorophosphate in the invention should be a salt of one or moremonofluorophosphate ions and/or difluorophosphate ions with one or moreions of at least one metal selected from Group 1, Group 2, and Group 13of the periodic table (hereinafter suitably referred to as “specificmetal”) or with a quaternary onium. The monofluorophosphate and/ordifluorophosphate may be one salt or may be any desired combination oftwo or more salts.

<1-3-1. Monofluorophosphoric Acid Metal Salt and Difluorophosphoric AcidMetal Salt>

First, an explanation is given on the case where the monofluorophosphateand difluorophosphate in the invention are a salt of one or moremonofluorophosphate ions or one or more difluorophosphate ions with oneor more specific-metal ions (hereinafter sometimes referred to as“monofluorophosphoric acid metal salt” and “difluorophosphoric acidmetal salt”, respectively).

Examples of the metals in Group 1 of the periodic table among thespecific metals usable in the monofluorophosphoric acid metal salt anddifluorophosphoric acid metal salt in the invention include lithium,sodium, potassium, and cesium. Preferred of these is lithium or sodium.Lithium is especially preferred.

Examples of the metals in Group 2 of the periodic table includemagnesium, calcium, strontium, and barium. Preferred of these ismagnesium or calcium. Magnesium is especially preferred.

Examples of the metals in Group 13 of the periodic table includealuminum, gallium, indium, and thallium. Preferred of these is aluminumor gallium. Aluminum is especially preferred.

The number of the atoms of such a specific metal possessed by onemolecule of the monofluorophosphoric acid metal salt ordifluorophosphoric acid metal salt in the invention is not limited. Thesalt may have only one atom of the specific metal or two or more atomsthereof.

In the case where the monofluorophosphoric acid metal salt or thedifluorophosphoric acid metal salt in the invention has two or morespecific-metal atoms per molecule, these specific-metal atoms may be ofthe same kind or may be of different kinds. Besides the specificmetal(s), one or more atoms of a metal other than the specific metalsmay be possessed.

Examples of the monofluorophosphoric acid metal salt anddifluorophosphoric acid metal salt include Li₂PO₃F, Na₂PO₃F, MgPO₃F,CaPO₃F, Al₂(PO₃F)₃, Ga₂ (PO₃F)₃, LiPO₂F₂, NaPO₂F₂, Mg(PO₂F₂)₂,Ca(PO₂F₂)₂, Al(PO₂F₂)₃, and Ga(PO₂F₂)₃. Preferred of these are Li₂PO₃F,LiPO₂F₂, NaPO₂F₂, and Mg(PO₂F₂)₂ and the like.

<1-3-2. Monofluorophosphoric Acid Quaternary Onium Salt andDifluorophosphoric Acid Quaternary Onium Salt>

An explanation is then given on the case where the monofluorophosphateand difluorophosphate in invention 1 to invention 6 are a salt of amonofluorophosphate ion or difluorophosphate ion with a quaternary onium(hereinafter sometimes referred to as “monofluorophosphoric acidquaternary onium salt” and “difluorophosphoric acid quaternary oniumsalt”, respectively).

The quaternary onium used in the monofluorophosphoric acid quaternaryonium salt and difluorophosphoric acid quaternary onium salt ininvention 1 to invention 6 usually is a cation. Examples thereof includecations represented by the following general formula (3).

In general formula (3), R¹ to R⁴ each independently represent ahydrocarbon group. The kind of this hydrocarbon group is not limited.Namely, the hydrocarbon group may be an aliphatic hydrocarbon group oran aromatic hydrocarbon group, or may be a hydrocarbon group includingthese two kinds of groups bonded to each other. In the case of analiphatic hydrocarbon group, this group may be an acyclic or cyclicgroup or may be a structure including an acyclic moiety and a cyclicmoiety bonded thereto. In the case of an acyclic hydrocarbon group, thisgroup may be linear or branched. The hydrocarbon group may be asaturated hydrocarbon group or may have an unsaturated bond.

Examples of the hydrocarbon groups represented by R¹ to R⁴ include alkylgroups, cycloalkyl groups, aryl groups, and aralkyl groups, and thelike.

Examples of the alkyl groups include

methyl, ethyl, 1-propyl, 1-methylethyl, 1-butyl, 1-methylpropyl,2-methylpropyl, and 1,1-dimethylethyl.

Preferred of these are methyl, ethyl, 1-propyl, 1-butyl, and the like.

Examples of the cycloalkyl groups include

cyclopentyl, 2-methylcyclopentyl, 3-methylcyclopentyl,2,2-dimethylcyclopentyl, 2,3-dimethylcyclopentyl,2,4-dimethylcyclopentyl, 2,5-dimethylcyclopentyl,3,3-dimethylcyclopentyl, 3,4-dimethylcyclopentyl, 2-ethylcyclopentyl,3-ethylcyclopentyl, cyclohexyl, 2-methylcyclohexyl, 3-methylcyclohexyl,4-methylcyclohexyl, 2,2-dimethylcyclohexyl, 2,3-dimethylcyclohexyl,2,4-dimethylcyclohexyl, 2,5-dimethylcyclohexyl, 2,6-dimethylcyclohexyl,3,4-dimethylcyclohexyl, 3,5-dimethylcyclohexyl, 2-ethylcyclohexyl,3-ethylcyclohexyl, 4-ethylcyclohexyl, bicyclo[3.2.1]oct-1-yl, andbicyclo[3.2.1]oct-2-yl, and the like.

Preferred of these are cyclopentyl, 2-methylcyclopentyl,3-methylcyclopentyl, cyclohexyl, 2-methylcyclohexyl, 3-methylcyclohexyl,4-methylcyclohexyl, and the like.

Examples of the aryl groups include

phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, and2,3-dimethylphenyl, and the like.

Preferred of these is phenyl.

Examples of the aralkyl groups include

phenylmethyl, 1-phenylethyl, 2-phenylethyl, diphenylmethyl, andtriphenylmethyl and the like.

Preferred of these are phenylmethyl and 2-phenylethyl.

The hydrocarbon groups represented by R¹ to R⁴ each may be substitutedwith one or more substituents. The kinds of the substituents are notlimited unless the substituents considerably lessen the effects ofinvention 1. Examples of the substituents include halogen atoms,hydroxyl, amino, nitro, cyano, carboxyl, ether groups, and aldehydegroups. In the case where the hydrocarbon group represented by each ofR¹ to R⁴ has two or more substituents, these substituents may be thesame or different.

When any two or more of the hydrocarbon groups represented by R¹ to R⁴are compared, the hydrocarbon groups may be the same or different. Whenthe hydrocarbon groups represented by R¹ to R⁴ have a substituent, thesesubstituted hydrocarbon groups including the substituents may be thesame or different. Furthermore, any desired two or more of thehydrocarbon groups represented by R¹ to R⁴ may be bonded to each otherto form a cyclic structure.

The number of carbon atoms of each of the hydrocarbon groups representedby R¹ to R⁴ is generally 1 or larger, and the upper limit thereof isgenerally 20 or smaller, preferably 10 or smaller, more preferably 5 orsmaller. When the number of carbon atoms thereof is too large, thenumber of moles per unit mass is too small and various effects tend tobe reduced. In the case where the hydrocarbon group represented by eachof R¹ to R⁴ has substituents, the number of carbon atoms of thesubstituted hydrocarbon group including these substituents is generallywithin that range.

In general formula (3), Q represents an atom belonging to Group 15 ofthe periodic table. Preferred of such atoms is a nitrogen atom orphosphorus atom.

In view of the above explanation, preferred examples of the quaternaryonium represented by general formula (3) include aliphatic acyclicquaternary salts, alicyclic ammoniums, alicyclic phosphoniums, andnitrogen-containing heterocyclic aromatic cations.

Especially preferred of the aliphatic acyclic quaternary salts aretetraalkylammoniums, tetraalkylphosphoniums, and the like.

Examples of the tetraalkylammoniums include

tetramethylammonium, ethyltrimethylammonium, diethyldimethylammonium,triethylmethylammonium, tetraethylammonium, and tetra-n-butylammonium,and the like.

Examples of the tetraalkylphosphoniums include

tetramethylphosphonium, ethyltrimethylphosphonium,diethyldimethylphosphonium, triethylmethylphosphonium,tetraethylphosphonium, and tetra-n-butylphosphonium, and the like.

Especially preferred of the alicyclic ammoniums are pyrrolidiniums,morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums,piperidiniums, and the like.

Examples of the pyrrolidiniums include

N,N-dimethylpyrrolidium, N-ethyl-N-methylpyrrolidium, andN,N-diethylpyrrolidium, and the like.

Examples of the morpholiniums include

N,N-dimethylmorpholinium, N-ethyl-N-methylmorpholinium, andN,N-diethylmorpholinium, and the like.

Examples of the imidazoliniums include

N,N′-dimethylimidazolinium, N-ethyl-N′-methylimidazolinium,N,N′-diethylimidazolinium, and 1,2,3-trimethylimidazolinium, and thelike.

Examples of the tetrahydropyrimidiniums include

N,N′-dimethyltetrahydropyrimidinium,N-ethyl-N′-methyltetrahydropyrimidinium,N,N′-diethyltetrahydropyrimidinium, and1,2,3-trimethyltetrahydropyrimidinium, and the like.

Examples of the piperaziniums include

N,N,N′,N′-tetramethylpiperazinium,N-ethyl-N,N′,N′-trimethylpiperazinium,N,N-diethyl-N′,N′-dimethylpiperazinium,N,N,N′-triethyl-N′-methylpiperazinium, andN,N,N′,N′-tetraethylpiperazinium, and the like.

Examples of the piperidiniums include

N,N-dimethylpiperidinium, N-ethyl-N-methylpiperidinium, andN,N-diethylpiperidinium, and the like.

Especially preferred of the nitrogen-containing heterocyclic aromaticcations are pyridiniums, imidazoliums, and the like.

Examples of the pyridiniums include

N-methylpyridinium, N-ethylpyridinium, 1,2-dimethylpyrimidinium,1,3-dimethylpyrimidinium, 1,4-dimethylpyrimidinium, and1-ethyl-2-methylpyrimidinium, and the like.

Examples of the imidazoliums include

N,N′-dimethylimidazolium, N-ethyl-N′-methylimidazolium,N,N′-diethylimidazolium, and 1,2,3-trimethylimidazolium and the like.

Namely, the salts of the quaternary oniums enumerated above with themonofluorophosphate ions and/or difluorophosphate ions enumerated aboveare preferred examples of the monofluorophosphoric acid quaternary oniumsalt and difluorophosphoric acid quaternary onium salt in the invention.

<1-3-3. Content, Detection (Derivation of Containment), Technical Range,etc.>

In the nonaqueous electrolyte of the invention, one monofluorophosphateor difluorophosphate only may be used or any desired combination of twoor more monofluorophosphates and/or difluorophosphates may be used inany desired proportion. However, from the standpoint of efficientlyoperating the nonaqueous-electrolyte secondary battery, it is preferredto use one monofluorophosphate or difluorophosphate.

The molecular weight of the monofluorophosphate or difluorophosphate isnot limited, and may be any desired value unless this considerablylessens the effects of the invention. However, the molecular weightthereof is generally 100 or higher. There is no particular upper limiton the molecular weight thereof. However, it is preferred that themolecular weight thereof should be generally 1,000 or lower, preferably500 or lower, because such a value is practicable in view of thereactivity of this reaction.

Usually, one salt of monofluorophosphoric acid or one salt ofdifluorophosphoric acid is used. However, in the case where it ispreferred to use a mixture of two or more salts in the nonaqueouselectrolyte to be prepared, a mixture of two or more ofmonofluorophosphates and difluorophosphates may be used.

The proportion of the monofluorophosphate and difluorophosphate in thenonaqueous electrolyte is preferably 10 ppm or higher (0.001% by mass orhigher), more preferably 0.01% by mass or higher, especially preferably0.05% by mass or higher, even more preferably 0.1% by mass or higher, interms of the total content of the salts based on the whole nonaqueouselectrolyte. The upper limit of the proportion of the sum of the saltsis preferably 5% by mass or lower, more preferably 4% by mass or lower,even more preferably 3% by mass or lower. When the concentration of themonofluorophosphate and the difluorophosphate is too low, there arecases where the effect of improving discharge load characteristics isdifficult to obtain. On the other hand, too high concentrations thereofmay lead to a decrease in charge/discharge efficiency.

When a nonaqueous electrolyte containing a monofluorophosphate and adifluorophosphate is subjected to the actual fabrication of anonaqueous-electrolyte secondary battery and the battery is disassembledto discharge the nonaqueous electrolyte again, then there are oftencases where the content of the salts in this nonaqueous electrolyte hasdecreased considerably. Consequently, the nonaqueous electrolytedischarged from a battery can be regarded as included in the inventionwhen at least one monofluorophosphate and/or difluorophosphate can bedetected in the electrolyte even in a slight amount. Furthermore, evenwhen a nonaqueous electrolyte containing a monofluorophosphate and adifluorophosphate is subjected to the actual fabrication of anonaqueous-electrolyte secondary battery and the nonaqueous electrolyterecovered by disassembling this battery and discharging the nonaqueouselectrolyte therefrom does not contain the monofluorophosphate and/ordifluorophosphate, then there are often cases where the phosphoric acidsalt is detected on the positive electrode, negative electrode, orseparator as another constituent member of the nonaqueous-electrolytesecondary battery. Consequently, when at least one monofluorophosphateand/or difluorophosphate has been detected in at least one constituentmember selected from the positive electrode, negative electrode, andseparator, this case also is regarded as included in the invention.

Moreover, when a monofluorophosphate and/or a difluorophosphate has beenincorporated into a nonaqueous electrolyte and has further beenincorporated into at least one constituted member selected from thepositive electrode, negative electrode, and separator, this case also isregarded as included in the invention.

On the other hand, a monofluorophosphate and/or a difluorophosphate maybe incorporated beforehand into an inner part or the surface of thepositive electrode of a nonaqueous-electrolyte secondary battery to befabricated. In this case, part or the whole of the monofluorophosphateand/or difluorophosphate which has been incorporated beforehand isexpected to dissolve in the nonaqueous electrolyte to perform thefunction thereof. This case also is regarded as included in theinvention.

Techniques for incorporating the salt beforehand into an inner part of apositive electrode or into the surface of a positive electrode are notparticularly limited. Examples thereof include: a method in which amonofluorophosphate and/or a difluorophosphate is dissolved beforehandin a slurry to be prepared in the production of a positive electrodewhich will be described later; and a method in which a solution preparedby dissolving a monofluorophosphate and/or a difluorophosphate in anydesired nonaqueous solvent beforehand is applied to or infiltrated intoa positive electrode which has been produced, and this electrode isdried to remove the solvent used and thereby incorporate the salt.

Furthermore, use may be made of a method in which anonaqueous-electrolyte secondary battery is actually fabricated using anonaqueous electrolyte containing at least one monofluorophosphateand/or difluorophosphate so that the salt is incorporated into an innerpart of the positive electrode or the surface of the positive electrodefrom the nonaqueous electrolyte. Since the nonaqueous electrolyte isinfiltrated into the positive electrode in fabricated anonaqueous-electrolyte secondary battery, there are often cases wherethe monofluorophosphate and difluorophosphate are contained in an innerpart of the positive electrode or in the surface of the positiveelectrode. Because of this, when at least a monofluorophosphate and/or adifluorophosphate can be detected in the positive electrode recoveredfrom a disassembled battery, this case is regarded as included in theinvention.

A monofluorophosphate and a difluorophosphate may be incorporatedbeforehand into an inner part or the surface of the negative electrodeof a nonaqueous-electrolyte secondary battery to be fabricated. In thiscase, part or the whole of the monofluorophosphate and/ordifluorophosphate which has been incorporated beforehand is expected todissolve in the nonaqueous electrolyte to perform the function thereof.This case is regarded as included in the invention. Techniques forincorporating the salt beforehand into an inner part of a negativeelectrode or into the surface of a negative electrode are notparticularly limited. Examples thereof include: a method in which amonofluorophosphate and a difluorophosphate are dissolved beforehand ina slurry to be prepared in the production of a negative electrode whichwill be described later; and a method in which a solution prepared bydissolving a monofluorophosphate and a difluorophosphate in any desirednonaqueous solvent beforehand is applied to or infiltrated into anegative electrode which has been produced, and this electrode is driedto remove the solvent used and thereby incorporate the salt.

Furthermore, use may be made of a method in which anonaqueous-electrolyte secondary battery is actually fabricated using anonaqueous electrolyte containing at least one monofluorophosphate anddifluorophosphate so that the salt is incorporated into an inner part ofthe negative electrode or the surface of the negative electrode from thenonaqueous electrolyte. Since the nonaqueous electrolyte is infiltratedinto the negative electrode in fabricated a nonaqueous-electrolytesecondary battery, there are often cases where the monofluorophosphateand difluorophosphate are contained in an inner part of the negativeelectrode or in the surface of the negative electrode. Because of this,when at least a monofluorophosphate and a difluorophosphate can bedetected in the negative electrode recovered from a disassembledbattery, this case is regarded as included in the invention.

A monofluorophosphate and/or a difluorophosphate may also beincorporated beforehand into an inner part or the surface of theseparator of a nonaqueous-electrolyte secondary battery to befabricated. In this case, part or the whole of the monofluorophosphateand difluorophosphate which have been incorporated beforehand isexpected to dissolve in the nonaqueous electrolyte to perform thefunction thereof. This case is regarded as included in the invention.Techniques for incorporating the salts beforehand into an inner part ofa separator or into the surface of a separator are not particularlylimited. Examples thereof include: a method in which amonofluorophosphate and a difluorophosphate are mixed beforehand duringseparator production; and a method in which a solution prepared bydissolving a monofluorophosphate and a difluorophosphate in any desirednonaqueous solvent beforehand is applied to or infiltrated into aseparator to be subjected to the fabrication of a nonaqueous-electrolytesecondary battery, and this separator is dried to remove the solventused and thereby incorporate the salt.

Furthermore, use may be made of a method in which anonaqueous-electrolyte secondary battery is actually fabricated using anonaqueous electrolyte containing a monofluorophosphate and/or adifluorophosphate so that the salt is incorporated into an inner part ofthe separator or the surface of the separator from the nonaqueouselectrolyte. Since the nonaqueous electrolyte is infiltrated into theseparator in fabricated a nonaqueous-electrolyte secondary battery,there are often cases where the monofluorophosphate anddifluorophosphate are contained in an inner part of the separator or inthe surface of the separator. Because of this, when at least amonofluorophosphate and a difluorophosphate can be detected in theseparator recovered from a disassembled battery, this case is regardedas included in the invention.

It is thought that when the monofluorophosphate and difluorophosphateare incorporated into a nonaqueous electrolyte together with a carbonatehaving a halogen atom, this nonaqueous electrolyte can improve thehigh-temperature storability of a nonaqueous-electrolyte secondarybattery employing the nonaqueous electrolyte. Factors in this have notbeen elucidated in detail. Although the scope of the invention is notconstrued as being limited by the factors, the following is thought. Themonofluorophosphate and/or difluorophosphate contained in the nonaqueouselectrolyte is thought to react with the carbonate having a halogen atomcontained therein to thereby form a satisfactory protective coatinglayer on the surface of the negative-electrode active material, and thisprotective coating layer is thought to inhibit side reactions to inhibitthe deterioration caused by high-temperature storage. It is also thoughtthat the coexistence of the monofluorophosphate and/or difluorophosphateand the carbonate having a halogen atom in the electrolyte contributesto an improvement in the properties of the protective coating film insome way.

<1-4. Additives>

The nonaqueous electrolyte of invention 1 may contain various additivesso long as these additives do not considerably lessen the effects ofinvention 1. In the case where additives are additionally incorporatedto prepare the nonaqueous electrolyte, conventionally known additivescan be used at will. One additive may be used alone, or any desiredcombination of two or more additives may be used in any desiredproportion.

Examples of the additives include overcharge inhibitors and aids forimproving capacity retentivity and cycle characteristics afterhigh-temperature storage. It is preferred to add a carbonate having anunsaturated bond (hereinafter sometimes referred to as “specificcarbonate”) as an aid for improving capacity retentivity and cyclecharacteristics after high-temperature storage, among those additives.The specific carbonate and other additives are separately explainedbelow.

<1-4-1. Specific Carbonate>

The specific carbonate is a carbonate having an unsaturated bond. Thespecific carbonate may have a halogen atom.

The molecular weight of the specific carbonate is not particularlylimited, and may be any desired value unless this considerably lessensthe effects of invention 1. However, the molecular weight thereof isgenerally 50 or higher, preferably 80 or higher, and is generally 250 orlower, preferably 150 or lower. When the molecular weight thereof is toohigh, this specific carbonate has reduced solubility in the nonaqueouselectrolyte and there are cases where the effect of the carbonate isdifficult to produce sufficiently.

Processes for producing the specific carbonate also are not particularlylimited, and a known process selected at will can be used to produce thecarbonate.

Any one specific carbonate may be incorporated alone into the nonaqueouselectrolyte of invention 1, or any desired combination of two or morespecific carbonates may be incorporated thereinto in any desiredproportion.

The amount of the specific carbonate to be incorporated into thenonaqueous electrolyte of invention 1 is not limited, and may be anydesired value unless this considerably lessens the effects ofinvention 1. It is, however, desirable that the specific carbonateshould be incorporated in a concentration which is generally 0.01% bymass or higher, preferably 0.1% by mass or higher, more preferably 0.3%by mass or higher, and is generally 70% by mass or lower, preferably 50%by mass or lower, more preferably 40% by mass or lower, based on thenonaqueous electrolyte of invention 1.

When the amount of the specific carbonate is below the lower limit ofthat range, there are cases where use of this nonaqueous electrolyte ofinvention 1 in a nonaqueous-electrolyte secondary battery results indifficulties in producing the effect of sufficiently improving the cyclecharacteristics of the nonaqueous-electrolyte secondary battery. On theother hand, when the proportion of the specific carbonate is too high,there is a tendency that use of this nonaqueous electrolyte of invention1 in a nonaqueous-electrolyte secondary battery results in decreases inthe high-temperature storability and continuous-charge characteristicsof the nonaqueous-electrolyte secondary battery. In particular, thereare cases where gas evolution is enhanced and capacity retentivitydecreases.

The specific carbonate according to invention 1 is not limited so longas it is a carbonate having one or more carbon-carbon unsaturated bonds,e.g., carbon-carbon double bonds or carbon-carbon triple bonds. Anydesired unsaturated carbonates may be used. Incidentally, carbonateshaving one or more aromatic rings are included in the carbonate havingan unsaturated bond.

Examples of the unsaturated carbonate include vinylene carbonate andderivatives thereof, ethylene carbonate derivatives substituted with oneor more aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond, phenyl carbonates, vinyl carbonates, andallyl carbonates, and the like.

Examples of the vinylene carbonate and derivatives thereof includevinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylenecarbonate, phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, andcatechol carbonate, and the like.

Examples of the ethylene carbonate derivatives substituted with one ormore aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond include vinylethylene carbonate,4,5-divinylethylene carbonate, phenylethylene carbonate, and4,5-diphenylethylene carbonate, and the like.

Examples of the phenyl carbonates include diphenyl carbonate, ethylphenyl carbonate, methyl phenyl carbonate, and t-butyl phenyl carbonate,and the like.

Examples of the vinyl carbonates include divinyl carbonate and methylvinyl carbonate, and the like.

Examples of the allyl carbonates include diallyl carbonate and allylmethyl carbonate.

Preferred of these specific carbonates are the vinylene carbonate andderivatives thereof and the ethylene derivatives substituted with one ormore aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond. In particular, vinylene carbonate,4,5-diphenylvinylene carbonate, 4,5-dimethylvinylene carbonate, andvinylethylene carbonate are more preferred because these carbonates forma stable interface-protective coating film.

<1-4-2. Other Additives>

Additives other than the specific carbonate are explained below.Examples of the additives other than the specific carbonate includeovercharge inhibitors and aids for improving capacity retentivity andcycle characteristics after high-temperature storage.

<1-4-2-1. Overcharge Inhibitors>

Examples of the overcharge inhibitors include

aromatic compounds including: toluene derivatives thereof, such astoluene and xylene; unsubstituted biphenyl or alkyl-substituted biphenylderivatives, such as biphenyl, 2-methylbiphenyl, 3-methylbiphenyl, and4-methylbiphenyl; unsubstituted terphenyls or alkyl-substitutedterphenyl derivatives, such as o-terphenyl, m-terphenyl, andp-terphenyl; partly hydrogenated unsubstituted terphenyls or partlyhydrogenated alkyl-substituted terphenyl derivatives; cycloalkylbenzenesand derivatives thereof, such as cyclopentylbenzene andcyclohexylbenzene; alkylbenzene derivatives having one or more tertiarycarbon atoms directly bonded to the benzene ring, such as cumene,1,3-diisopropylbenzene, and 1,4-diisopropylbenzene; alkylbenzenederivatives having a quaternary carbon atom directly bonded to thebenzene ring, such as t-butylbenzene, t-amylbenzene, and t-hexylbenzene;and aromatic compounds having an oxygen atom, such as diphenyl ether anddibenzofuran, and the like.

Other examples of the overcharge inhibitors include

products of the partial fluorination of aromatic compounds shown above,such as fluorobenzene, fluorotoluene, benzotrifluoride,2-fluorobiphenyl, o-cyclohexylfluorobenzene, andp-cyclohexylfluorobenzene; and fluorine-containing anisole compoundssuch as 2,4-difluoroanisole, 2,5-difluoroanisole, and1,6-difluoroanisole, and the like.

One of those overcharge inhibitors may be used alone, or any desiredcombination of two or more thereof may be used in any desiredproportion. In the case of employing any desired combination, compoundsin the same class among those enumerated above may be used incombination or compounds in different classes may be used incombination.

Examples of the case where compounds in different classes are used incombination include

a toluene derivative and a biphenyl derivative; a toluene derivative anda terphenyl derivative; a toluene derivative and a partly hydrogenatedterphenyl derivative; a toluene derivative and a cycloalkylbenzenederivative; a toluene derivative and an alkylbenzene derivative havingone or more tertiary carbon atoms directly bonded to the benzene ring; atoluene derivative and an alkylbenzene derivative having a quaternarycarbon atom directly bonded to the benzene ring; a toluene derivativeand an aromatic compound having an oxygen atom; a toluene derivative anda partly fluorinated aromatic compound; a toluene derivative and afluorine-containing anisole compound; a biphenyl derivative and aterphenyl derivative; a biphenyl derivative and a partly hydrogenatedterphenyl derivative; a biphenyl derivative and a cycloalkylbenzenederivative; a biphenyl derivative and an alkylbenzene derivative havingone or more tertiary carbon atoms directly bonded to the benzene ring; abiphenyl derivative and an alkylbenzene derivative having a quaternarycarbon atom directly bonded to the benzene ring; a biphenyl derivativeand an aromatic compound having an oxygen atom; a biphenyl derivativeand a partly fluorinated aromatic compound; a biphenyl derivative and afluorine-containing anisole compound; a terphenyl derivative and apartly hydrogenated terphenyl derivative; a terphenyl derivative and acycloalkylbenzene derivative; a terphenyl derivative and an alkylbenzenederivative having one or more tertiary carbon atoms directly bonded tothe benzene ring; a terphenyl derivative and an alkylbenzene derivativehaving a quaternary carbon atom directly bonded to the benzene ring; aterphenyl derivative and an aromatic compound having an oxygen atom; aterphenyl derivative and a partly fluorinated aromatic compound; aterphenyl derivative and a fluorine-containing anisole compound; apartly hydrogenated terphenyl derivative and a cycloalkylbenzenederivative; a partly hydrogenated terphenyl derivative and analkylbenzene derivative having one or more tertiary carbon atomsdirectly bonded to the benzene ring; a partly hydrogenated terphenylderivative and an alkylbenzene derivative having a quaternary carbonatom directly bonded to the benzene ring; a partly hydrogenatedterphenyl derivative and an aromatic compound having an oxygen atom; apartly hydrogenated terphenyl derivative and a partly fluorinatedaromatic compound; a partly hydrogenated terphenyl derivative and afluorine-containing anisole compound; a cycloalkylbenzene derivative andan alkylbenzene derivative having one or more tertiary carbon atomsdirectly bonded to the benzene ring; a cycloalkylbenzene derivative andan alkylbenzene derivative having a quaternary carbon atom directlybonded to the benzene ring; a cycloalkylbenzene derivative and anaromatic compound having an oxygen atom; a cycloalkylbenzene derivativeand a partly fluorinated aromatic compound; a cycloalkylbenzenederivative and a fluorine-containing anisole compound; an alkylbenzenederivative having one or more tertiary carbon atoms directly bonded tothe benzene ring and an alkylbenzene derivative having a quaternarycarbon atom directly bonded to the benzene ring; an alkylbenzenederivative having one or more tertiary carbon atoms directly bonded tothe benzene ring and an aromatic compound having an oxygen atom; analkylbenzene derivative having one or more tertiary carbon atomsdirectly bonded to the benzene ring and a partly fluorinated aromaticcompound; an alkylbenzene derivative having one or more tertiary carbonatoms directly bonded to the benzene ring and a fluorine-containinganisole compound; an alkylbenzene derivative having a quaternary carbonatom directly bonded to the benzene ring and an aromatic compound havingan oxygen atom; an alkylbenzene derivative having a quaternary carbonatom directly bonded to the benzene ring and a partly fluorinatedaromatic compound; an alkylbenzene derivative having a quaternary carbonatom directly bonded to the benzene ring and a fluorine-containinganisole compound; an aromatic compound having an oxygen atom and apartly fluorinated aromatic compound; an aromatic compound having anoxygen atom and a fluorine-containing anisole compound; and a partlyfluorinated aromatic compound and a fluorine-containing anisolecompound.

Specific examples thereof include

a combination of biphenyl and o-terphenyl, a combination of biphenyl andm-terphenyl, a combination of biphenyl and a partly hydrogenatedterphenyl derivative, a combination of biphenyl and cumene, acombination of biphenyl and cyclopentylbenzene, a combination ofbiphenyl and cyclohexylbenzene, a combination of biphenyl andt-butylbenzene, a combination of biphenyl and t-amylbenzene, acombination of biphenyl and diphenyl ether, a combination of biphenyland dibenzofuran, a combination of biphenyl and fluorobenzene, acombination of biphenyl and benzotrifluoride, a combination of biphenyland 2-fluorobiphenyl, a combination of biphenyl ando-fluorocyclohexylbenzene, a combination of biphenyl andp-fluorocyclohexylbenzene, a combination of biphenyl and2,4-difluoroanisole,a combination of o-terphenyl and a partly hydrogenated terphenylderivative, a combination of o-terphenyl and cumene, a combination ofo-terphenyl and cyclopentylbenzene, a combination of o-terphenyl andcyclohexylbenzene, a combination of o-terphenyl and t-butylbenzene, acombination of o-terphenyl and t-amylbenzene, a combination ofo-terphenyl and diphenyl ether, a combination of o-terphenyl anddibenzofuran, a combination of o-terphenyl and fluorobenzene, acombination of o-terphenyl and benzotrifluoride, a combination ofo-terphenyl and 2-fluorobiphenyl, a combination of o-terphenyl ando-fluorocyclohexylbenzene, a combination of o-terphenyl andp-fluorocyclohexylbenzene, a combination of o-terphenyl and2,4-difluoroanisole,a combination of m-terphenyl and a partly hydrogenated terphenylderivative, a combination of m-terphenyl and cumene, a combination ofm-terphenyl and cyclopentylbenzene, a combination of m-terphenyl andcyclohexylbenzene, a combination of m-terphenyl and t-butylbenzene, acombination of m-terphenyl and t-amylbenzene, a combination ofm-terphenyl and diphenyl ether, a combination of m-terphenyl anddibenzofuran, a combination of m-terphenyl and fluorobenzene, acombination of m-terphenyl and benzotrifluoride, a combination ofm-terphenyl and 2-fluorobiphenyl, a combination of m-terphenyl ando-fluorocyclohexylbenzene, a combination of m-terphenyl andp-fluorocyclohexylbenzene, a combination of m-terphenyl and2,4-difluoroanisole,a combination of a partly hydrogenated terphenyl derivative and cumene,a combination of a partly hydrogenated terphenyl derivative andcyclopentylbenzene, a combination of a partly hydrogenated terphenylderivative and cyclohexylbenzene, a combination of a partly hydrogenatedterphenyl derivative and t-butylbenzene, a combination of a partlyhydrogenated terphenyl derivative and t-amylbenzene, a combination of apartly hydrogenated terphenyl derivative and diphenyl ether, acombination of a partly hydrogenated terphenyl derivative anddibenzofuran, a combination of a partly hydrogenated terphenylderivative and fluorobenzene, a combination of a partly hydrogenatedterphenyl derivative and benzotrifluoride, a combination of a partlyhydrogenated terphenyl derivative and 2-fluorobiphenyl, a combination ofa partly hydrogenated terphenyl derivative ando-fluorocyclohexylbenzene, a combination of a partly hydrogenatedterphenyl derivative and p-fluorocyclohexylbenzene, a combination of apartly hydrogenated terphenyl derivative and 2,4-difluoroanisole,a combination of cumene and cyclopentylbenzene, a combination of cumeneand cyclohexylbenzene, a combination of cumene and t-butylbenzene, acombination of cumene and t-amylbenzene, a combination of cumene anddiphenyl ether, a combination of cumene and dibenzofuran, a combinationof cumene and fluorobenzene, a combination of cumene andbenzotrifluoride, a combination of cumene and 2-fluorobiphenyl, acombination of cumene and o-fluorocyclohexylbenzene, a combination ofcumene and p-fluorocyclohexylbenzene, a combination of cumene and2,4-difluoroanisole,a combination of cyclohexylbenzene and t-butylbenzene, a combination ofcyclohexylbenzene and t-amylbenzene, a combination of cyclohexylbenzeneand diphenyl ether, a combination of cyclohexylbenzene and dibenzofuran,a combination of cyclohexylbenzene and fluorobenzene, a combination ofcyclohexylbenzene and benzotrifluoride, a combination ofcyclohexylbenzene and 2-fluorobiphenyl, a combination ofcyclohexylbenzene and o-fluorocyclohexylbenzene, a combination ofcyclohexylbenzene and p-fluorocyclohexylbenzene, a combination ofcyclohexylbenzene and 2,4-difluoroanisole,a combination of t-butylbenzene and t-amylbenzene, a combination oft-butylbenzene and diphenyl ether, a combination of t-butylbenzene anddibenzofuran, a combination of t-butylbenzene and fluorobenzene, acombination of t-butylbenzene and benzotrifluoride, a combination oft-butylbenzene and 2-fluorobiphenyl, a combination of t-butylbenzene ando-fluorocyclohexylbenzene, a combination of t-butylbenzene andp-fluorocyclohexylbenzene, a combination of t-butylbenzene and2,4-difluoroanisole,a combination of t-amylbenzene and diphenyl ether, a combination oft-amylbenzene and dibenzofuran, a combination of t-amylbenzene andfluorobenzene, a combination of t-amylbenzene and benzotrifluoride, acombination of t-amylbenzene and 2-fluorobiphenyl, a combination oft-amylbenzene and o-fluorocyclohexylbenzene, a combination oft-amylbenzene and p-fluorocyclohexylbenzene, a combination oft-amylbenzene and 2,4-difluoroanisole,a combination of diphenyl ether and dibenzofuran, a combination ofdiphenyl ether and fluorobenzene, a combination of diphenyl ether andbenzotrifluoride, a combination of diphenyl ether and 2-fluorobiphenyl,a combination of diphenyl ether and o-fluorocyclohexylbenzene, acombination of diphenyl ether and p-fluorocyclohexylbenzene, acombination of diphenyl ether and 2,4-difluoroanisole,a combination of dibenzofuran and fluorobenzene, a combination ofdibenzofuran and benzotrifluoride, a combination of dibenzofuran and2-fluorobiphenyl, a combination of dibenzofuran ando-fluorocyclohexylbenzene, a combination of dibenzofuran andp-fluorocyclohexylbenzene, a combination of dibenzofuran and2,4-difluoroanisole,a combination of fluorobenzene and benzotrifluoride, a combination offluorobenzene and 2-fluorobiphenyl, a combination of fluorobenzene ando-fluorocyclohexylbenzene, a combination of fluorobenzene andp-fluorocyclohexylbenzene, a combination of fluorobenzene and2,4-difluoroanisole,a combination of benzotrifluoride and 2-fluorobiphenyl, a combination ofbenzotrifluoride and o-fluorocyclohexylbenzene, a combination ofbenzotrifluoride and p-fluorocyclohexylbenzene, a combination ofbenzotrifluoride and 2,4-difluoroanisole,a combination of 2-fluorobiphenyl and o-fluorocyclohexylbenzene, acombination of 2-fluorobiphenyl and p-fluorocyclohexylbenzene, acombination of 2-fluorobiphenyl and 2,4-difluoroanisole,a combination of o-fluorocyclohexylbenzene andp-fluorocyclohexylbenzene, a combination of o-fluorocyclohexylbenzeneand 2,4-difluoroanisole, and a combination of p-fluorocyclohexylbenzeneand 2,4-difluoroanisole, and the like.

In the case where nonaqueous electrolyte 1 of the invention contains anovercharge inhibitor, the concentration thereof may be any value unlessthis considerably lessens the effects of the invention 1. It is,however, desirable that the concentration thereof should be regulated soas to be in the range of generally from 0.1% by mass to 5% by mass basedon the whole nonaqueous electrolyte.

To incorporate an overcharge inhibitor into nonaqueous electrolyte 1 ofthe invention in such an amount as not to considerably lessen theeffects of invention 1 is preferred because the nonaqueous-electrolytesecondary battery has improved safety even if overcharged due to anerroneous usage or under a situation in which an overcharge protectioncircuit does not work normally, such as, e.g., charger abnormality.

<1-4-2-2. Aids for Improving Capacity Retentivity and CycleCharacteristics after High-Temperature Storage>

Examples of the aids for improving capacity retentivity and cyclecharacteristics after high-temperature storage include

the anhydrides of dicarboxylic acids such as succinic acid, maleic acid,and phthalic acid;

carbonate compounds other than the specific carbonates, such aserythritan carbonate and spiro-bis-dimethylene carbonate;sulfur-containing compounds such as ethylene sulfite,1,3-propanesultone, 1,4-butanesultone, methyl methanesulfonate,busulfan, sulfolane, sulfolene, dimethyl sulfone, diphenyl sulfone,methyl phenyl sulfone, dibutyl disulfide, dicyclohexyl disulfide,tetramethylthiuram monosulfide, N,N-dimethylmethanesulfonamide, andN,N-diethylmethanesulfonamide;nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone,1-methyl-2-piperidone, 3-methyl-2-oxazolidinone,1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide;hydrocarbon compounds such as heptane, octane, and cycloheptane; andfluorine-containing aromatic compounds such as fluorobenzene,difluorobenzene, and benzotrifluoride.[2. Nonaqueous-Electrolyte Secondary Battery]

The nonaqueous-electrolyte secondary battery of this invention isconstituted of the nonaqueous electrolyte of the invention describedabove and a positive electrode and a negative electrode which arecapable of occluding and releasing ions. The nonaqueous-electrolytesecondary battery of the invention may be equipped with otherconstitutions.

<2-1. Battery Constitution>

The constitution of the nonaqueous-electrolyte secondary battery of theinvention, excluding the negative electrode and the nonaqueouselectrolyte, may be the same as that of conventionally knownnonaqueous-electrolyte secondary batteries. Usually, the battery of theinvention has a constitution including a positive electrode and anegative electrode which have been superposed through a porous film(separator) impregnated with the nonaqueous electrolyte of theinvention, the electrodes and the separator being held in a case.Consequently, the shape of the nonaqueous-electrolyte secondary batteryof the invention is not particularly limited, and may be any of thecylindrical type, prismatic type, laminate type, coin type, large type,and the like.

<2-2. Nonaqueous Electrolyte>

As the nonaqueous electrolyte, the nonaqueous electrolyte of theinvention described above is used. Incidentally, a mixture of thenonaqueous electrolyte of the invention and another nonaqueouselectrolyte may be used so long as this is not counter to the spirit ofthe invention.

<2-3. Negative Electrode>

Negative-electrode active materials usable in the negative electrode aredescribed below.

The negative-electrode active materials are not particularly limited solong as these are capable of electrochemically occluding/releasinglithium ions. Examples thereof include a carbonaceous material, an alloymaterial, and a lithium-containing metal composite oxide material.

<2-3-1. Carbonaceous Material>

The carbonaceous material to be used as a negative-electrode activematerial preferably is one which is selected from:

(1) natural graphites;

(2) artificial carbonaceous substances and carbonaceous materialsobtained by subjecting artificial graphitic substances to a heattreatment at a temperature in the range of 400-3,200° C. one or moretimes;

(3) carbonaceous materials giving a negative-electrode active-materiallayer which is composed of at least two carbonaceous substancesdiffering in crystallinity and/or has an interface where at least twocarbonaceous substances differing in crystallinity are in contact witheach other; and(4) carbonaceous materials giving a negative-electrode active-materiallayer which is composed of at least two carbonaceous substancesdiffering in orientation and/or has an interface where at least twocarbonaceous substances differing in orientation are in contact witheach other. This is because this carbonaceous material brings about asatisfactory balance between initial irreversible capacity andhigh-current-density charge/discharge characteristics. One of thecarbonaceous materials (1) to (4) may be used alone, or any desiredcombination of two or more thereof in any desired proportion may beused.

Examples of the artificial carbonaceous substances and artificialgraphitic substances in (2) above include natural graphites, coal coke,petroleum coke, coal pitch, petroleum pitch, carbonaceous substancesobtained by oxidizing these pitches, needle coke, pitch coke, carbonmaterials obtained by partly graphitizing these cokes, products of thepyrolysis of organic substances, such as furnace black, acetylene black,and pitch-derived carbon fibers, organic substances capable ofcarbonization and products of the carbonization thereof, or solutionsobtained by dissolving any of such organic substances capable ofcarbonization in a low-molecular organic solvent, e.g., benzene,toluene, xylene, quinoline, or n-hexane, and products of thecarbonization of these solutions.

Examples of the organic substances capable of carbonization include coaltar pitches ranging from soft pitch to hard pitch, coal-derived heavyoil such as dry distillation/liquefaction oil, straight-run heavy oilsuch as topping residues and vacuum distillation residues, heavy oilsresulting from petroleum cracking, such as ethylene tar as a by-productof the thermal cracking of crude oil, naphtha, etc., aromatichydrocarbons such as acenaphthylene, decacyclene, anthracene, andphenanthrene, nitrogen-atom-containing heterocyclic compounds such asphenazine and acridine, sulfur-atom-containing heterocyclic compoundssuch as thiophene and bithiophene, polyphenylenes such as biphenyl andterphenyl, poly(vinyl chloride), poly(vinyl alcohol), poly(vinylbutyral), substances obtained by insolubilizing these compounds,nitrogen-containing organic polymers such as polyacrylonitrile andpolypyrrole, sulfur-containing organic polymers such as polythiophene,organic polymers such as polystyrene, natural polymers such aspolysaccharides represented by cellulose, lignin, mannan,poly(galacturonic acid), chitosan, and saccharose, thermoplastic resinssuch as poly(phenylene sulfide) and poly(phenylene oxide), andthermosetting resins such as furfuryl alcohol resins,phenol-formaldehyde resins, and imide resins, and the like.

<2-3-2. Constitution and Properties of Carbonaceous Negative Electrodeand Method of Preparation Thereof>

With respect to the properties of the carbonaceous material, negativeelectrode containing the carbonaceous material, method of electrodeformation, current collector, and nonaqueous-electrolyte secondarybattery, it is desirable that any one of the following (1) to (21)should be satisfied or two or more thereof be simultaneously satisfied.

(1) X-Ray Parameter

The carbonaceous material preferably has a value of d (interplanarspacing) for the lattice planes (002), as determined by X-raydiffractometry in accordance with the method of the Japan Society forPromotion of Scientific Research, of generally 0.335-0.340 nm,especially 0.335-0.338 nm, in particular 0.335-0.337 nm. The crystallitesize (Lc) thereof, as determined by X-ray diffractometry in accordancewith the method of the Japan Society for Promotion of ScientificResearch, is generally 1.0 nm or larger, preferably 1.5 nm or larger,especially preferably 2 nm or larger.

A preferred material obtained by coating the surface of a graphite withamorphous carbon is one which is constituted of a graphite having avalue of d for the lattice planes (002) as determined by X-raydiffractometry of 0.335-0.338 nm as a core material and, adherent to thesurface thereof, a carbonaceous material having a larger value of d forthe lattice planes (002) as determined by X-ray diffractometry than thecore material, and in which the proportion of the core material to thecarbonaceous material having a larger value of d for the lattice planes(002) as determined by X-ray diffractometry than the core material isfrom 99/1 to 80/20 in terms of weight ratio. By using this material, anegative electrode which has a high capacity and is less apt to reactwith the electrolyte can be produced.

(2) Ash Content

The ash content of the carbonaceous material is preferably 1% by mass orlower, especially 0.5% by mass or lower, in particular 0.1% by mass orlower, based on the whole carbonaceous material. The lower limit of theash content thereof is preferably at least 1 ppm by mass of the wholecarbonaceous material. When the ash content by mass thereof exceeds theupper limit of that range, there are cases where battery performancedeterioration caused by reaction with the nonaqueous electrolyte duringcharge/discharge becomes not negligible. When the ash content thereof islower than the lower limit of that range, there are cases where theproduction of this carbonaceous material necessitates much time andenergy and an apparatus for pollution prevention, resulting in anincrease in cost.

(3) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the carbonaceousmaterial, the volume-average particle diameter (median diameter) thereofas determined by the laser diffraction/scattering method is generally 1μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger,especially preferably 7 μm or larger, and is generally 100 μm orsmaller, preferably 50 lam or smaller, more preferably 40 μm or smaller,even more preferably 30 μm or smaller, especially preferably 25 μm orsmaller. When the volume-average particle diameter thereof is smallerthan the lower limit of that range, there are cases where irreversiblecapacity increases, leading to a loss in initial battery capacity. Whenthe volume-average particle diameter thereof exceeds the upper limit ofthat range, there are cases where such a carbonaceous material isundesirable from the standpoint of battery production because an unevencoating surface is apt to result when an electrode is produced throughcoating fluid application.

Volume-average particle diameter is determined by dispersing the carbonpowder in a 0.2% by mass aqueous solution (about 10 mL) ofpoly(oxyethylene(20)) sorbitan monolaurate as a surfactant and examiningthe dispersion with a laser diffraction/scattering type particle sizedistribution analyzer (LA-700, manufactured by HORIBA, Ltd.). The mediandiameter determined through this measurement is defined as thevolume-average particle diameter of the carbonaceous material in theinvention.

(4) Raman R Value, Raman Half-Value Width

The Raman R value of the carbonaceous material as determined by theargon ion laser Raman spectroscopy is generally 0.01 or higher,preferably 0.03 or higher, more preferably 0.1 or higher, and isgenerally 1.5 or lower, preferably 1.2 or lower, more preferably 1 orlower, especially preferably 0.5 or lower.

When the Raman R value thereof is lower than the lower limit of thatrange, the surface of such particles has too high crystallinity andthere are cases where the number of intercalation sites into whichlithium comes with charge/discharge decreases. Namely, there are caseswhere suitability for charge decreases. In addition, when a coatingfluid containing such a carbonaceous material is applied to a currentcollector and the resultant coating is pressed to heighten the densityof the negative electrode, then the crystals are apt to orient indirections parallel to the electrode plate and this may lead to adecrease in load characteristics. On the other hand, when the Raman Rvalue thereof exceeds the upper limit of that range, the surface of suchparticles has reduced crystallinity and enhanced reactivity with thenonaqueous electrolyte and this may lead to a decrease in efficiency andenhanced gas evolution.

The Raman half-value width around 1,580 cm⁻¹ of the carbonaceousmaterial is not particularly limited. However, the half-value widththereof is generally 10 cm⁻¹ or larger, preferably 15 cm⁻¹ or larger,and is generally 100 cm⁻¹ or smaller, preferably 80 cm⁻¹ or smaller,more preferably 60 cm⁻¹ or smaller, especially preferably 40 cm⁻¹ orsmaller. When the Raman half-value width thereof is smaller than thelower limit of that range, the surface of such particles has too highcrystallinity and there are cases where the number of intercalationsites into which lithium comes with charge/discharge decreases. Namely,there are cases where suitability for charge decreases. In addition,when a coating fluid containing such a carbonaceous material is appliedto a current collector and the resultant coating is pressed to heightenthe density of the negative electrode, then the crystals are apt toorient in directions parallel to the electrode plate and this may leadto a decrease in load characteristics. On the other hand, when the Ramanhalf-value width thereof exceeds the upper limit of that range, thesurface of such particles has reduced crystallinity and enhancedreactivity with the nonaqueous electrolyte and this may lead to adecrease in efficiency and enhanced gas evolution.

The examination for a Raman spectrum is made with a Raman spectrometer(Raman spectrometer manufactured by Japan Spectroscopic Co., Ltd.). Inthe examination, a sample is charged into a measuring cell by causingthe sample to fall naturally into the cell and the surface of the samplein the cell is irradiated with argon ion laser light while rotating thecell in a plane perpendicular to the laser light. The Raman spectrumobtained is examined for the intensity I_(A) of a peak P_(A) around1,580 cm⁻¹ and the intensity I_(B) of a peak P_(B) around 1,360 cm⁻¹.The ratio between these intensities R(R=I_(B)/I_(A)) is calculated. TheRaman R value calculated through this examination is defined as theRaman R value of the carbonaceous material in the invention.Furthermore, the half-value width of the peak P_(A) around 1,580 cm⁻¹ inthe Raman spectrum obtained is measured, and this value is defined asthe Raman half-value width of the carbonaceous material in theinvention.

Conditions for the Raman spectroscopy are as follows.

Wavelength of argon ion laser: 514.5 nm

Laser power on sample: 15-25 mW

Resolution: 10-20 cm⁻¹

Examination range: 1,100 cm⁻¹ to 1,730 cm⁻¹

Analysis for Raman R value and Raman half-value width: backgroundprocessing

Smoothing: simple average; convolution, 5 points

(5) BET Specific Surface Area

The BET specific surface area of the carbonaceous material, in terms ofthe value of specific surface area as determined by the BET method, isgenerally 0.1 m²·g⁻¹ or larger, preferably 0.7 m²·g⁻¹ or larger, morepreferably 1.0 m²·g⁻¹ or larger, especially preferably 1.5 m²·g⁻¹ orlarger, and is generally 100 m²·g⁻¹ or smaller, preferably 25 m²·g⁻¹ orsmaller, more preferably 15 m²·g⁻¹ or smaller, especially preferably 10m²·g⁻¹ or smaller. When the BET specific surface area thereof is smallerthan the lower limit of that range, use of this carbonaceous material asa negative-electrode material is apt to result in poor lithiumacceptance during charge and in lithium deposition on the electrodesurface. Consequently, there is the possibility of resulting in reducedstability. On the other hand, when the specific surface area thereofexceeds the upper limit of that range, there are cases where use of thiscarbonaceous material as a negative-electrode material is apt to resultin enhanced reactivity with the nonaqueous electrolyte and enhanced gasevolution and a preferred battery is difficult to obtain.

The determination of specific surface area by the BET method is madewith a surface area meter (a fully automatic surface area measuringapparatus manufactured by Ohukura Riken Co., Ltd.) by preliminarilydrying a sample at 350° C. for 15 minutes in a nitrogen stream and thenmeasuring the specific surface area thereof by the gas-flowing nitrogenadsorption BET one-point method using a nitrogen/helium mixture gasprecisely regulated so as to have a nitrogen pressure of 0.3 relative toatmospheric pressure. The specific surface area determined through thismeasurement is defined as the BET specific surface area of thecarbonaceous material in the invention.

(6) Pore Diameter Distribution

The pore diameter distribution of the carbonaceous material iscalculated through a measurement of the amount of intruded mercury. Itis desirable that the carbonaceous material should have a pore diameterdistribution in which the amount of interstices which correspond topores having a diameter of from 0.01 μm to 1 μm and which include poreswithin the particles, particle surface irregularities formed by steps,and pores attributable to contact surfaces among the particles, asdetermined by mercury porosimetry (mercury intrusion method), isgenerally 0.01 cm³·g⁻¹ or larger, preferably 0.05 cm³·g⁻¹ or larger,more preferably 0.1 cm³·g⁻¹ or larger, and is generally 0.6 cm³·g⁻¹ orsmaller, preferably 0.4 cm³·g⁻¹ or smaller, more preferably 0.3 cm³·g⁻¹or smaller. When the pore diameter distribution thereof is larger thanthe upper limit of that range, there are cases where a large amount of abinder is necessary in electrode plate formation. When the amount ofinterstices thereof is smaller than the lower limit of that range, thereare cases where high-current-density charge/discharge characteristicsdecrease and the effect of diminishing electrode expansion/contractionduring charge/discharge is not obtained.

The total volume of pores thereof corresponding to the pore diameterrange of from 0.01 μm to 100 μm, as determined by mercury porosimetry(mercury intrusion method), is generally 0.1 cm³·g⁻¹ or larger,preferably 0.25 cm³·g⁻¹ or larger, more preferably 0.4 cm³·g⁻¹ orlarger, and is generally 10 cm³·g⁻¹ or smaller, preferably 5 cm³·g⁻¹ orsmaller, more preferably 2 cm³·g⁻¹ or smaller. When the total porevolume thereof exceeds the upper limit of that range, there are caseswhere a large amount of a binder is necessary in electrode plateformation. When the total pore volume thereof is smaller than the lowerlimit of that range, there are cases where the dispersing effect of athickener or binder in electrode plate formation is not obtained.

The average pore diameter thereof is generally 0.05 μm or larger,preferably 0.1 μm or larger, more preferably 0.5 μm or larger, and isgenerally 50 μm or smaller, preferably 20 μm or smaller, more preferably10 μm or smaller. When the average pore diameter thereof exceeds theupper limit of that range, there are cases where a large amount of abinder is necessary. When the average pore diameter thereof is smallerthan the lower limit of that range, there are cases wherehigh-current-density charge/discharge characteristics decrease.

The amount of mercury intruded is measured with a mercury porosimeter(Autopore 9520, manufactured by Micromeritics Corp.) as an apparatus forthe mercury porosimetry. A sample is pretreated by placing about 0.2 gof the sample in a powder cell, closing the cell, and degassing thesample at room temperature under vacuum (50 μmHg or lower) for 10minutes. Subsequently, the pressure in the cell is reduced to 4 psia(about 28 kPa) and mercury is introduced thereinto. The internalpressure is stepwise elevated from 4 psia (about 28 kPa) to 40,000 psia(about 280 MPa) and then lowered to 25 psia (about 170 kPa). The numberof steps in the pressure elevation is 80 or larger. In each step, theamount of mercury intruded is measured after an equilibrium time of 10seconds.

A pore diameter distribution is calculated from the mercury intrusioncurve thus obtained, using the Washburn equation. Incidentally, thesurface tension (γ) and contact angle (Ψ) of mercury are taken as 485dyne·cm⁻¹ (1 dyne=10 μN) and 140°, respectively. The average porediameter used is the pore diameter corresponding to a cumulative porevolume of 50%.

(7) Roundness

When the carbonaceous material is examined for roundness as an index tothe degree of sphericity thereof, the roundness thereof is preferablywithin the range shown below. Roundness is defined by “Roundness=(lengthof periphery of equivalent circle having the same area as projectedparticle shape)/(actual length of periphery of projected particleshape)”. When a particle has a roundness of 1, this particletheoretically is a true sphere.

The closer to 1 the roundness of carbonaceous-material particles havinga particle diameter in the range of 3-40 μm, the more the particles aredesirable. The roundness of the particles is desirably 0.1 or higher,preferably 0.5 or higher, more preferably 0.8 or higher, even morepreferably 0.85 or higher, especially preferably 0.9 or higher.

The higher the roundness, the more the high-current-densitycharge/discharge characteristics are improved. Consequently, when theroundness of the carbonaceous-material particles is lower than the lowerlimit of that range, there are cases where the negative-electrode activematerial has reduced suitability for loading and interparticleresistance is increased, resulting in reduced short-timehigh-current-density charge/discharge characteristics.

Roundness is determined with a flow type particle image analyzer (FPIA,manufactured by Sysmex Industrial Corp.). About 0.2 g of a sample isdispersed in a 0.2% by mass aqueous solution (about 50 mL) ofpoly(oxyethylene(20)) sorbitan monolaurate as a surfactant, and anultrasonic wave of 28 kHz is propagated to the dispersion for 1 minuteat an output of 60 W. Thereafter, particles having a particle diameterin the range of 3-40 μm are examined with the analyzer having adetection range set at 0.6-400 μm. The roundness determined through thismeasurement is defined as the roundness of the carbonaceous material inthe invention.

Methods for improving roundness are not particularly limited. However, acarbonaceous material in which the particles have been rounded by arounding treatment is preferred because it gives an electrode in whichthe interstices among particles are uniform in shape. Examples of therounding treatment include: a method in which a shear force orcompressive force is applied to thereby mechanically make the shape ofthe particles close to sphere; and a method of mechanical/physicaltreatment in which fine particles are aggregated into particles by meansof the bonding force of a binder or of the fine particles themselves.

(8) True Density

The true density of the carbonaceous material is generally 1.4 g·cm⁻³ orhigher, preferably 1.6 g·cm⁻³ or higher, more preferably 1.8 g·cm⁻³ orhigher, especially preferably 2.0 g·cm⁻³ or higher, and is generally2.26 g·cm³ or lower. When the true density of the carbonaceous materialis lower than the lower limit of that range, there are cases where thiscarbon has too low crystallinity, resulting in an increase in initialirreversible capacity. Incidentally, the upper limit of that range is atheoretical value of the true density of graphites.

The true density of the carbonaceous material is determined by theliquid-phase displacement method (pyconometer method) using butanol. Thevalue determined through this measurement is defined as the true densityof the carbonaceous material in the invention.

(9) Tap Density

The tap density of the carbonaceous material is generally 0.1 g·cm⁻³ orhigher, preferably 0.5 g·cm⁻³ or higher, more preferably 0.7 g·cm⁻³ orhigher, especially preferably 1 g·cm⁻³ or higher, and is preferably 2g·cm⁻³ or lower, more preferably 1.8 g·cm⁻³ or lower, especiallypreferably 1.6 g·cm⁻³ or lower. When the tap density thereof is lowerthan the lower limit of that range, there are cases where thiscarbonaceous material, when used in a negative electrode, is less apt tohave a high loading density and cannot give a battery having a highcapacity. On the other hand, when the tap density thereof exceeds theupper limit of that range, the amount of interparticle interstices inthe electrode is too small and it is difficult to secure electricalconductivity among the particles. There are hence cases where preferredbattery performances are difficult to obtain.

Tap density is determined by dropping a sample through a sieve having anopening size of 300 μm into a 20 cm³ tapping cell to fill the cell withthe sample up to the brim, subsequently conducting tapping operations1,000 times over a stroke length of 10 mm using a powder densimeter(e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), andcalculating the tap density from the resultant volume of the sample andthe weight thereof. The tap density calculated through this measurementis defined as the tap density of the carbonaceous material in theinvention.

(10) Orientation Ratio

The orientation ratio of the carbonaceous material is generally 0.005 orhigher, preferably 0.01 or higher, more preferably 0.015 or higher, andis generally 0.67 or lower. When the orientation ratio thereof is lowerthan the lower limit of that range, there are cases where high-densitycharge/discharge characteristics decrease. The upper limit of that rangeis a theoretical upper limit of the orientation ratio of carbonaceousmaterials.

Orientation ratio is determined by X-ray diffractometry after a sampleis molded by compaction. A molding obtained by packing 0.47 g of asample into a molding machine having a diameter of 17 mm and compactingthe sample at 58.8 MN·m⁻² is set with clay on a sample holder forexamination so as to be flush with the holder. This sample molding isexamined for X-ray diffraction. From the intensities of the resultant(110) diffraction peak and (004) diffraction peak for the carbon, theratio represented by (110) diffraction peak intensity/(004) diffractionpeak intensity is calculated. The orientation ratio calculated throughthis measurement is defined as the orientation ratio of the carbonaceousmaterial in the invention.

Conditions for the X-ray diffractometry are as follows. Incidentally,“2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator

Slit:

-   -   Divergence slit=0.5 degrees    -   Receiving slit=0.15 mm    -   Scattering slit=0.5 degrees

Examination range and step angle/measuring time:

-   -   (110) plane: 75°≦2θ≦80° 1°/60 sec    -   (004) plane: 52°≦2θ≦57° 1°/60 sec        (11) Aspect Ratio (Powder)

The aspect ratio of the carbonaceous material is generally 1 or higher,and is generally 10 or lower, preferably 8 or lower, more preferably 5or lower. When the aspect ratio thereof exceeds the upper limit of thatrange, there are cases where this carbonaceous material causes streaklines in electrode plate formation and an even coating surface cannot beobtained, resulting in a decrease in high-current-densitycharge/discharge characteristics. Incidentally, the lower limit of thatrange is a theoretical lower limit of the aspect ratio of carbonaceousmaterials.

In determining aspect ratio, particles of the carbonaceous material areexamined with a scanning electron microscope with enlargement. Fifty arearbitrarily selected from graphite particles fixed to an edge face of ametal having a thickness of 50 μm or smaller, and each particle isexamined in a three-dimensional manner while rotating or inclining thestage to which the sample is fixed. In this examination, the length ofthe longest axis A of each carbonaceous-material particle and the lengthof the shortest axis B perpendicular to that axis are measured, and theaverage of the A/B values is determined. The aspect ratio (A/B)determined through this measurement is defined as the aspect ratio ofthe carbonaceous material in the invention.

(12) Minor-Material Mixing

Minor-material mixing means that the negative electrode and/or thenegative-electrode active material contains two or more carbonaceousmaterials differing in property. The term property herein means one ormore properties selected from the group consisting of X-ray diffractionparameter, median diameter, aspect ratio, BET specific surface area,orientation ratio, Raman R value, tap density, true density, poredistribution, roundness, and ash content.

Especially preferred examples of the minor-material mixing include: onein which the volume-based particle size distribution is not symmetricalabout the median diameter; one in which two or more carbonaceousmaterials differing in Raman R value are contained; and one in whichcarbonaceous materials differing in X-ray parameter are contained.

One example of the effects of the minor-material mixing is that theincorporation of a carbonaceous material, such as a graphite, e.g., anatural graphite or artificial graphite, or an amorphous carbon, e.g., acarbon black such as acetylene black or needle coke, as a conductivematerial serves to reduce electrical resistance.

In the case where conductive materials are incorporated asminor-material mixing, one conductive material may be incorporated aloneor any desired combination of two or more conductive materials in anydesired proportion may be incorporated. The proportion of the conductivematerial(s) to be incorporated is generally 0.1% by mass or higher,preferably 0.5% by mass or higher, more preferably 0.6% by mass orhigher, and is generally 45% by mass or lower, preferably 40% by mass orlower, based on the carbonaceous material. When the proportion thereofis lower than the lower limit of that range, there are cases where theeffect of improving conductivity is difficult to obtain. Proportionsthereof exceeding the upper limit of that range may lead to an increasein initial irreversible capacity.

(13) Electrode Production

Any known method can be used for electrode production unless thisconsiderably lessens the effects of the invention. For example, a binderand a solvent are added to a negative-electrode active materialoptionally together with a thickener, conductive material, filler, etc.to obtain a slurry and this slurry is applied to a current collector anddried. Thereafter, the coated current collector is pressed, whereby anelectrode can be formed.

The thickness of the negative-electrode active-material layer per oneside in the stage just before the step of injecting a nonaqueouselectrolyte in battery fabrication is generally 15 μm or larger,preferably 20 μm or larger, more preferably 30 μm or larger, and isgenerally 150 μM or smaller, preferably 120 μm or smaller, morepreferably 100 μm or smaller. The reasons for this are as follows. Whenthe thickness of the negative-electrode active-material layer is largerthan the upper limit of that range, a nonaqueous electrolyte is less aptto infiltrate into around the interface of the current collector and,hence, there are cases where high-current-density charge/dischargecharacteristics decrease. When the thickness thereof is smaller than thelower limit of that range, the proportion by volume of the currentcollector to the negative-electrode active material increases and thereare cases where battery capacity decreases. The negative-electrodeactive material may be roller-pressed to obtain a sheet electrode, ormay be subjected to compression molding to obtain a pellet electrode.

(14) Current Collector

As the current collector for holding the negative-electrode activematerial, a known one can be used at will. Examples of the currentcollector for the negative electrode include metallic materials such ascopper, nickel, stainless steel, and nickel-plated steel. Copper isespecially preferred from the standpoints of processability and cost.

In the case where the current collector is a metallic material, examplesof the shape of the current collector include metal foils, metalcylinders, metal coils, metal plates, thin metal films, expanded metals,punching metals, and metal foams. Preferred of these are thin metalfilms. More preferred are copper foils. Even more preferred are a rolledcopper foil, which is produced by the rolling process, and anelectrolytic copper foil, which is produced by the electrolytic process.Either of these can be used as a current collector.

In the case of a copper foil having a thickness smaller than 25 μm, usecan be made of a copper alloy (e.g., phosphor bronze, titanium-copper,Corson alloy, or Cu—Cr—Zr alloy) having a higher strength than purecopper.

The current collector constituted of a copper foil produced by therolling process is less apt to crack even when the negative electrode isrolled tightly or rolled at an acute angle, because the copper crystalsare oriented in the rolling direction. This current collector can beadvantageously used in small cylindrical batteries.

The electrolytic copper foil is obtained by immersing a metallic drum ina nonaqueous electrolyte containing copper ions dissolved therein,causing current to flow through the system while rotating the drum tothereby deposit copper on the drum surface, and peeling the copperdeposit from the drum. Copper may be deposited on a surface of therolled copper foil by the electrolytic process. One or each side of sucha copper foil may have undergone a surface-roughening treatment or asurface treatment (e.g., a chromate treatment in a thickness of fromseveral nanometers to about 1 μm or a priming treatment with titanium).

The current collector base is desired to further have the followingproperties.

(14-1) Average Surface Roughness (Ra)

The average surface roughness (Ra) of that side of the current collectorbase on which a thin negative-electrode active-material film is to beformed, as determined by the method provided for in JIS B 0601-1994, isnot particularly limited. However, the average surface roughness thereofis generally 0.05 μm or higher, preferably 0.1 μm or higher, morepreferably 0.15 μm or higher, and is generally 1.5 μm or lower,preferably 1.3 μm or lower, more preferably 1.0 μm or lower. This isbecause when the average surface roughness (Ra) of the current collectorbase is within that range, satisfactory charge/discharge cyclecharacteristics can be expected. In addition, the area of the interfacebetween the base and a thin negative-electrode active-material film isincreased and adhesion to the thin negative-electrode active-materialfilm is improved. The upper limit of the average surface roughness (Ra)thereof is not particularly limited. However, a current collector basehaving an Ra of 1.5 μm or lower is usually employed because a foilhaving a practical thickness for batteries and having an average surfaceroughness (Ra) exceeding 1.5 μm is generally difficult to procure.

(14-2) Tensile Strength

Tensile strength is a quotient obtained by dividing the maximum tensileforce required before test piece breakage by the sectional area of thetest piece. In the invention, the tensile strength is determined througha measurement conducted with the same apparatus and by the same methodas those described in JIS Z 2241 (Method of Metallic-Material TensileTest).

The tensile strength of the current collector base is not particularlylimited. However, it is generally 100 N·mm⁻² or higher, preferably 250N·mm⁻² or higher, more preferably 400 N·mm⁻² or higher, especiallypreferably 500 N·mm⁻² or higher. The higher the tensile strength, themore the current collector base is preferred. However, the tensilestrength thereof is generally 1,000 N·mm⁻² or lower from the standpointof industrial availability. A current collector base having a hightensile strength can be inhibited from cracking with theexpansion/contraction of the thin negative-electrode active-materialfilm which occur upon charge/discharge. With this current collectorbase, satisfactory cycle characteristics can be obtained.

(14-3) 0.2% Proof Stress

The term 0.2% proof stress means the degree of load necessary forimparting a plastic (permanent) deformation of 0.2%. Namely, it meansthat application of that degree of load and subsequent removal thereofresult in a 0.2% deformation. The 0.2% proof stress is determinedthrough a measurement conducted with the same apparatus and by the samemethod as for tensile strength.

The 0.2% proof stress of the current collector base is not particularlylimited. However, it is desirable that the 0.2% proof stress thereofshould be generally 30 N·mm⁻² or higher, preferably 150 N·mm⁻² orhigher, especially preferably 300 N/mm² or higher. The higher the 0.2%proof stress, the more the current collector base is preferred. However,the 0.2% proof stress thereof is generally desirably 900 N·mm⁻² or lowerfrom the standpoint of industrial availability. A current collector basehaving a high 0.2% proof stress can be inhibited from plasticallydeforming with the expansion/contraction of the thin negative-electrodeactive-material film which occur upon charge/discharge. With thiscurrent collector base, satisfactory cycle characteristics can beobtained.

(14-4) Thickness of Current Collector

The current collector may have any desired thickness. However, thethickness thereof is generally 1 μm or larger, preferably 3 μm orlarger, more preferably 5 μm or larger, and is generally 1 mm orsmaller, preferably 100 μm or smaller, more preferably 50 μm or smaller.In case where the current collector is thinner than 1 μm, this collectorhas reduced strength and there are hence cases where coating isdifficult. When the current collector is thicker than 100 μm, there arecases where this collector deforms an electrode shape, e.g., a rolledform. The current collector may be in a mesh form.

(15) Thickness Ratio Between Current Collector and Negative-ElectrodeActive-Material Layer

The thickness ratio between the current collector and thenegative-electrode active-material layer is not particularly limited.However, the value of “(thickness of the negative-electrodeactive-material layer on one side just before impregnation with thenonaqueous electrolyte)/(thickness of the current collector)” ispreferably 150 or smaller, more preferably 20 or smaller, especiallypreferably 10 or smaller, and is preferably 0.1 or larger, morepreferably 0.4 or larger, especially preferably 1 or larger.

When the thickness ratio between the current collector and thenegative-electrode active-material layer exceeds the upper limit of thatrange, there are cases where this current collector heats up due toJoule's heat during high-current-density charge/discharge. When thatratio decreases beyond the lower limit of that range, the proportion byvolume of the current collector to the negative-electrode activematerial increases and this may reduce the capacity of the battery.

(16) Electrode Density

When the negative-electrode active material is used to form anelectrode, the electrode structure is not particularly limited. However,the density of the negative-electrode active material present on thecurrent collector is preferably 1 g·cm⁻³ or higher, more preferably 1.2g·cm⁻³ or higher, especially preferably 1.3 g·cm⁻³ or higher, and ispreferably 2 g·cm⁻³ or lower, more preferably 1.9 g·cm⁻³ or lower, evenmore preferably 1.8 g·cm⁻³ or lower, especially preferably 1.7 g·cm⁻³ orlower. When the density of the negative-electrode active materialpresent on the current collector exceeds the upper limit of that range,there are cases where the negative-electrode active-material particlesare broken and this increases the initial irreversible capacity andreduces the infiltration of a nonaqueous electrolyte into around thecurrent collector/negative-electrode active material interface. As aresult, high-current-density charge/discharge characteristics maydecrease. When the density thereof is lower than the lower limit of thatrange, there are cases where electrical conductivity among thenegative-electrode active-material particles decreases and thisincreases battery resistance, resulting in a reduced capacity per unitvolume.

(17) Binder

The binder for binding the negative-electrode active material is notparticularly limited so long as it is stable to the nonaqueouselectrolyte and to the solvent to be used for electrode production.

Examples thereof include resinous polymers such as polyethylene,polypropylene, poly(ethylene terephthalate), poly(methyl methacrylate),aromatic polyamides, cellulose, and nitrocellulose; rubbery polymerssuch as SBR (styrene/butadiene rubbers), isoprene rubbers, butadienerubbers, fluororubbers, NBR (acrylonitrile/butadiene rubbers), andethylene/propylene rubbers; styrene/butadiene/styrene block copolymersor products of hydrogenation thereof; thermoplastic elastomeric polymerssuch as EPDM (ethylene/propylene/diene terpolymers),styrene/ethylene/butadiene/styrene copolymers, andstyrene/isoprene/styrene block copolymers or products of hydrogenationthereof; flexible resinous polymers such as syndiotactic1,2-polybutadiene, poly(vinyl acetate), ethylene/vinyl acetatecopolymers, and propylene/α-olefin copolymers; fluorochemical polymerssuch as poly(vinylidene fluoride), polytetrafluoroethylene, fluorinatedpoly(vinylidene fluoride), and polytetrafluoroethylene/ethylenecopolymers; and polymer compositions having the property of conductingalkali metal ions (especially lithium ions). One of these may be usedalone, or any desired combination of two or more thereof in any desiredproportion may be used.

The kind of the solvent to be used for forming a slurry is notparticularly limited so long as it is a solvent in which thenegative-electrode active material and binder and the thickener andconductive material which are optionally used according to need can bedissolved or dispersed. Either an aqueous solvent or an organic solventmay be used.

Examples of the aqueous solvent include water and alcohols. Examples ofthe organic solvent include N-methylpyrrolidone (NMP),dimethylformamide, dimethylacetamide, methyl ethyl ketone,cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine,N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone,diethyl ether, dimethylacetamide, hexamethylphosphoramide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, andhexane, and the like.

Especially when an aqueous solvent is used, it is preferred to add adispersant or the like in combination with a thickener and prepare aslurry using a latex of, e.g., SBR. One of those solvents may be usedalone, or any desired combination of two or more thereof in any desiredproportion may be used.

The proportion of the binder to the negative-electrode active materialis preferably 0.1% by mass or higher, more preferably 0.5% by mass orhigher, especially preferably 0.6% by mass or higher, and is preferably20% by mass or lower, more preferably 15% by mass or lower, even morepreferably 10% by mass or lower, especially preferably 8% by mass orlower. In case where the proportion of the binder to thenegative-electrode active material exceeds the upper limit of thatrange, the proportion of the binder which does not contribute to batterycapacity increases and this may lead to a decrease in battery capacity.When the binder amount is small than the lower limit of that range,there are cases where the negative electrode has a reduced strength.

Especially when the binder includes a rubbery polymer represented by SBRas the main component, the proportion of this binder to thenegative-electrode active material is generally 0.1% by mass or higher,preferably 0.5% by mass or higher, more preferably 0.6% by mass orhigher, and is generally 5% by mass or lower, preferably 3% by mass orlower, more preferably 2% by mass or lower.

In the case where the binder includes a fluorochemical polymerrepresented by poly(vinylidene fluoride) as the main component, theproportion of this binder to the negative-electrode active material isgenerally 1% by mass or higher, preferably 2% by mass or higher, morepreferably 3% by mass or higher, and is generally 15% by mass or lower,preferably 10% by mass or lower, more preferably 8% by mass or lower.

A thickener is used generally for the purpose of regulating the slurryviscosity. The thickener is not particularly limited. Examples thereofinclude carboxymethyl cellulose, methyl cellulose, hydroxymethylcellulose, ethyl cellulose, poly(vinyl alcohol), oxidized starch,phosphorylated starch, casein, and salts of these. One of thesethickeners may be used alone, or any desired combination of two or morethereof in any desired proportion may be used.

In the case where such a thickener is further added, the proportion ofthe thickener to the negative-electrode active material is generally0.1% by mass or higher, preferably 0.5% by mass or higher, morepreferably 0.6% by mass or higher, and is generally 5% by mass or lower,preferably 3% by mass or lower, more preferably 2% by mass or lower.When the proportion of the thickener to the negative-electrode activematerial is lower than the lower limit of that range, there are caseswhere applicability decreases considerably. Proportions thereofexceeding the upper limit of that range result in a reduced proportionof the negative-electrode active material in the negative-electrodeactive-material layer, and this may pose a problem that battery capacitydecreases and a problem that resistance among the particles of thenegative-electrode active material increases.

(18) Orientation Ratio in Electrode Plate

The orientation ratio in the electrode plate is generally 0.001 orhigher, preferably 0.005 or higher, more preferably 0.01 or higher, andis generally 0.67 or lower. When the orientation ratio therein is lowerthan the lower limit of that range, there are cases where high-densitycharge/discharge characteristics decrease. The upper limit of that rangeis a theoretical upper limit of orientation ratio incarbonaceous-material electrodes.

An examination for determining the orientation ratio in the electrodeplate is as follows. The negative electrode which has been pressed to atarget density is examined by X-ray diffractometry to determine theorientation ratio of the negative-electrode active material in thiselectrode. Although specific techniques therefor are not particularlylimited, a standard method is as follows. The peaks attributable to the(110) diffraction and (004) diffraction of the carbon obtained by X-raydiffractometry are subjected to peak separation by fitting withasymmetric Pearson VII as a profile function. Thus, the integratedintensities of the (110) diffraction and (004) diffraction peaks arecalculated. From the integrated intensities obtained, the ratiorepresented by (integrated intensity of (110) diffraction)/(integratedintensity of (004) diffraction) is calculated. The negative-electrodeactive-material orientation ratio for the electrode thus calculated isdefined as the orientation ratio in the electrode plate employing thecarbonaceous material in the invention.

Conditions for this X-ray diffractometry are as follows. Incidentally,“20” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator

Slit:

-   -   Divergence slit=1 degree    -   Receiving slit=0.1 mm    -   Scattering slit=1 degree

Examination range and step angle/measuring time:

-   -   (110) plane: 76.5°≦2θ≦78.5° 0.01°/3 sec    -   (004) plane: 53.5°≦2θ≦56.0° 0.01°/3 sec

Sample preparation:

The electrode is fixed to a glass plate with a double-facedpressure-sensitive adhesive tape having a thickness of 0.1 mm.

<2-3-3. Metal Compound Material, Constitution and Properties of NegativeElectrode Employing Metal Compound Material, and Method of PreparationThereof>

The metal compound material to be used as a negative-electrode activematerial is not particularly limited so long as the material is capableof occluding/releasing lithium. Use may be made of an elemental metal oralloy which forms a lithium alloy or any of compounds thereof, such asoxides, carbides, nitrides, silicides, sulfides, and phosphides.Examples of such metal compounds include compounds containing a metalsuch as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, orZn. In particular, the negative-electrode active material preferably isan elemental metal or alloy which forms a lithium alloy. It is preferredthat the active material should be a material containing any of themetals and semimetals in Group 13 and Group 14 (i.e., carbon isexcluded). Furthermore, it is preferred that the active material shouldbe an elemental metal selected from silicon (Si), tin (Sn), and lead(Pb) (hereinafter, these meals are often referred to as “specificmetallic elements”) or an alloy or compound containing one or more atomsof any of these metals. One of such material may be used alone, or anydesired combination of two or more of these in any desired proportionmay be used.

Examples of the negative-electrode active material including atoms of atleast one member selected from the specific metallic elements include:the elemental metal which is any one of the specific metallic elements;alloys constituted of two or more specific metal elements; alloysconstituted of one or more specific metal elements and one or moremetallic elements of another kind; compounds containing one or morespecific metallic elements; and composite compounds, e.g., oxides,carbides, nitrides, silicides, sulfides, or phosphides, of thesecompounds. By using any of these elemental metals, alloys, and metalcompounds as a negative-electrode active material, a battery having ahigher capacity can be obtained.

Examples of the negative-electrode active material further includecompounds formed by the complicated bonding of any of those compositecompounds to one or more elemental metals or alloys or to severalelements, e.g., nonmetallic elements. More specifically, in the case ofsilicon and tin, for example, it is able to use an alloy of thoseelements with a metal which does not function as a negative electrode.In the case of tin, for example, it is able to use a complicatedcompound constituted of a combination of five to six elements includingtin, a metal which functions as a negative electrode and is not silicon,a metal which does not function as a negative electrode, and anonmetallic element.

Preferred of those negative-electrode active materials are the elementalmetal which is any one of the specific metallic elements, alloys of twoor more of the specific metallic elements, and oxides, carbides,nitrides, and other compounds of the specific metallic elements. This isbecause these negative-electrode active materials give a battery havinga high capacity per unit weight. Especially preferred are the elementalmetal(s), alloys, oxides, carbides, nitrides, and the like of siliconand/or tin from the standpoints of capacity per unit weight andenvironmental burden.

The following compounds containing silicon and/or tin also are preferredbecause these compounds bring about excellent cycle characteristics,although inferior in capacity per unit mass to the elemental metals oralloys thereof.

A silicon and/or tin oxide in which the elemental ratio of the siliconand/or tin to the oxygen is generally 0.5 or higher, preferably 0.7 orhigher, more preferably 0.9 or higher, and is generally 1.5 or lower,preferably 1.3 or lower, more preferably 1.1 or lower.

A silicon and/or tin nitride in which the elemental ratio of the siliconand/or tin to the nitrogen is generally 0.5 or higher, preferably 0.7 orhigher, more preferably 0.9 or higher, and is generally 1.5 or lower,preferably 1.3 or lower, more preferably 1.1 or lower.

A silicon and/or tin carbide in which the elemental ratio of the siliconand/or tin to the carbon is generally 0.5 or higher, preferably 0.7 orhigher, more preferably 0.9 or higher, and is generally 1.5 or lower,preferably 1.3 or lower, more preferably 1.1 or lower.

Any one of the negative-electrode active materials described above maybe used alone, or any desired combination of two or more thereof in anydesired proportion may be used.

The negative electrode in the nonaqueous-electrolyte secondary batteryof this invention can be produced by any known method. Examples ofmethods for negative-electrode production include: a method in which abinder, a conductive material, and other ingredients are added to any ofthe negative-electrode active materials described above and this mixtureis directly pressed by roller to form a sheet electrode; and a method inwhich the mixture is compression-molded to form a pellet electrode.Usually, however, use is made of a method in which a thin film layercontaining any of the negative-electrode active materials describedabove (negative-electrode active-material layer) is formed on a currentcollector for negative electrodes (hereinafter sometimes referred to as“negative-electrode current collector”) by a technique such as, e.g.,coating fluid application, vapor deposition, sputtering, or plating. Inthis case, a negative-electrode active-material layer may be formed on anegative-electrode current collector by adding a binder, thickener,conductive material, solvent, etc. to the negative-electrode activematerial to obtain a mixture in a slurry form, applying this mixture tothe negative-electrode current collector, drying the mixture applied,and then pressing the coated current collector to densify the coating.

Examples of the material of the negative-electrode current collectorinclude copper, copper alloys, nickel, nickel alloys, and stainlesssteel. Copper foils are preferred of these materials from thestandpoints of processability into thin films and cost.

The thickness of the negative-electrode current collector is generally 1μm or larger, preferably 5 μm or larger, and is generally 100 μm orsmaller, preferably 50 μm or smaller. The reasons for this are asfollows. In case where the negative-electrode current collector is toothick, this may result in too large a decrease in the capacity of thewhole battery. Conversely, in case where the current collector is toothin, this collector may be difficult to handle.

It is preferred that the surface of each of those negative-electrodecurrent collectors should be subjected to a surface-roughening treatmentbeforehand in order to improve the effect of binding thenegative-electrode active-material layer to be formed on the surface.Examples of techniques for the surface roughening include blasting,rolling press with a roll having a roughened surface, and mechanicalpolishing in which the collector surface is polished with an abrasivecloth or paper having abrasive particles fixed thereto, a grindstone, anemery wheel, a wire brush equipped with steel bristles, or the like.Examples thereof further include electrolytic polishing and chemicalpolishing.

It is also possible to use a negative-electrode current collector of theperforated type, such as an expanded metal or a punching metal, as anegative-electrode current collector having a reduced weight in order toimprove energy density per unit weight of the battery. Anegative-electrode current collector of this type can be varied inweight at will by changing the percentage of openings thereof.Furthermore, in the case where a negative-electrode active-materiallayer is formed on each side of a negative-electrode current collectorof this type, the negative-electrode active-material layers are evenless apt to peel off because of the effect of ribetting through theholes. It should, however, be noted that too high a percentage ofopenings results in a reduced contact area between eachnegative-electrode active-material layer and the negative-electrodecurrent collector and hence in reduced, rather than increased adhesionstrength.

The slurry for forming a negative-electrode active-material layer isgenerally produced by adding a binder, a thickener, etc. to anegative-electrode material. The term “negative-electrode material” inthis description means a material including both a negative-electrodeactive material and a conductive material.

It is preferred that the content of the negative-electrode activematerial in the negative-electrode material should be generally 70% bymass or higher, especially 75% by mass or higher, and be generally 97%by mass or lower, especially 95% by mass or lower. The reasons for thisare as follows. In case where the content of the negative-electrodeactive material is too low, a secondary battery employing the resultantnegative electrode tends to have an insufficient capacity. In case wherethe content thereof is too high, the relative content of the binder andother components is insufficient and this tends to result ininsufficient strength of the negative electrode obtained. When two ormore negative-electrode active materials are used in combination, thiscombination may be used so that the total amount of thenegative-electrode active materials satisfies that range.

Examples of the conductive material for use in the negative electrodeinclude metallic materials such as copper and nickel, and carbonmaterials such as graphites and carbon blacks. One of these materialsmay be used alone, or any desired combination of two or more thereof inany desired proportion may be used. In particular, use of a carbonmaterial as the conductive material is preferred because the carbonmaterial functions also as an active material. It is preferred that thecontent of the conductive material in the negative electrode should begenerally 3% by mass or higher, especially 5% by mass or higher, and begenerally 30% by mass or lower, especially 25% by mass or lower. Thereasons for this are as follows. In case where the content of theconductive material is too low, conductivity tends to be insufficient.In case where the content thereof is too high, the relative content ofthe negative-electrode active material and other components isinsufficient and this tends to result in decreases in battery capacityand strength. When two or more conductive materials are used incombination, this combination may be used so that the total amount ofthe conductive materials satisfies that range.

As the binder for the negative electrode, any desired binder can be usedso long as it is safe for the solvent to be used in electrode productionand for the electrolyte. Examples thereof include poly(vinylidenefluoride), polytetrafluoroethylene, polyethylene, polypropylene,styrene/butadiene rubbers, isoprene rubbers, butadiene rubbers,ethylene/acrylic acid copolymers, and ethylene/methacrylic acidcopolymers. One of these binders may be used alone, or any desiredcombination of two or more thereof in any desired proportion may beused. It is preferred that the content of the binder should be generally0.5 parts by weight or larger, especially 1 part by weight or larger,and be generally 10 parts by weight or smaller, especially 8 parts byweight or smaller, per 100 parts by weight of the negative-electrodematerial. The reasons for this are as follows. In case where the contentof the binder is too low, the resultant electrode tends to haveinsufficient strength. In case where the content thereof is too high,the relative content of the negative-electrode active material and othercomponents is insufficient and this tends to result in insufficientbattery capacity and insufficient conductivity. When two or more bindersare used in combination, this combination may be used so that the totalamount of the binders satisfies that ranges.

Examples of the thickener for use in the negative electrode includecarboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose,ethyl cellulose, poly(vinyl alcohol), oxidized starch, phosphorylatedstarch, and casein. One of these thickeners may be used alone, or anydesired combination of two or more thereof in any desired proportion maybe used. A thickener may be used according to need. In the case of usinga thickener, it is preferred to use the thickener so that the contentthereof in the negative-electrode active-material layer is in the rangeof generally from 0.5% by mass to 5% by mass.

The slurry for forming a negative-electrode active-material layer isprepared by mixing the negative-electrode active material with aconductive material, a binder, and a thickener according to need usingan aqueous solvent or an organic solvent as a dispersion medium. Wateris generally used as the aqueous solvent. However, a solvent other thanwater, such as an alcohol, e.g., ethanol, a cyclic amide, e.g.,N-methylpyrrolidone, or the like, can be used in combination with waterin a proportion of up to about 30% by mass based on the water. Examplesof the organic solvent usually include cyclic amides such asN-methylpyrrolidone, acyclic amides such as N,N-dimethylformamide andN,N-dimethylacetamide, aromatic hydrocarbons such as anisole, toluene,and xylene, and alcohols such as butanol and cyclohexanol. Preferred ofthese are cyclic amides such as N-methylpyrrolidone and acyclic amidessuch as N,N-dimethylformamide and N,N-dimethylacetamide. Any one of suchsolvents may be used alone, or any desired combination of two or morethereof in any desired proportion may be used.

The viscosity of the slurry is not particularly limited so long as theslurry is applicable to a current collector. The slurry may be suitablyprepared while changing the amount of the solvent to be used, etc. sothat the slurry is applicable.

The slurry obtained is applied to the negative-electrode currentcollector described above, and the coated collector is dried and thenpressed, whereby a negative-electrode active-material layer is formed.Techniques for the application are not particularly limited, and atechnique which itself is known can be employed. Techniques for thedrying also are not particularly limited, and use can be made of a knowntechnique such as, e.g., natural drying, drying by heating, or vacuumdrying.

The negative-electrode active material is used to produce an electrodein the manner described above. The structure of this electrode is notparticularly limited. However, the density of the active materialpresent on the current collector is preferably 1 g·cm⁻³ or higher, morepreferably 1.2 g·cm⁻³ or higher, especially preferably 1.3 g·cm⁻³ orhigher, and is preferably 2 g·cm⁻³ or lower, more preferably 1.9 g·cm⁻³or lower, even more preferably 1.8 g·cm⁻³ or lower, especiallypreferably 1.7 g·cm⁻³ or lower. When the density of the active materialpresent on the current collector exceeds the upper limit of that range,there are cases where particles of the active material are destroyed andthis causes an increase in initial irreversible capacity and reduces theinfiltration of the nonaqueous electrolyte into around the currentcollector/active material interface, resulting in impairedhigh-current-density charge/discharge characteristics. When the densitythereof is lower than the lower limit of that range, there are caseswhere conductivity between particles of the active material decreases,resulting in increased battery resistance and reduced capacity per unitvolume.

<2-3-4. Lithium-Containing Metal Composite Oxide Material, Constitutionand Properties of Negative Electrode Employing Lithium-Containing MetalComposite Oxide Material, and Method of Preparation Thereof>

The lithium-containing metal composite oxide material to be used as anegative-electrode active material is not particularly limited so longas the material is capable of occluding/releasing lithium. However, alithium-containing composite metal oxide material containing titanium ispreferred, and a composite oxide of lithium and titanium (hereinafterabbreviated to “lithium-titanium composite oxide”) is more preferred.Namely, use of a lithium-titanium composite oxide having a spinelstructure is especially preferred because incorporation of thiscomposite oxide into a negative-electrode active material fornonaqueous-electrolyte secondary batteries is effective in considerablyreducing output resistance.

Also preferred are lithium-titanium composite oxides in which thelithium or titanium has been replaced by one or more other metallicelements, e.g., at least one element selected from the group consistingof Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.

Such metal oxide preferably is a lithium-titanium composite oxiderepresented by general formula (4) wherein 0.7≦x≦1.5, 1.5≦y≦2.3, and0≦z≦1.6, because the structure thereof is stable during lithium iondoping/undoping.Li_(x)Ti_(y)M_(z)O₄  (4)[In general formula (4), M represents at least one element selected fromthe group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, andNb.]

Of the compositions represented by general formula (4), structuresrepresented by general formula (4) wherein

(a) 1.2≦x≦1.4, 1.5≦y≦1.7, and z=0

(b) 0.9≦x≦1.1, 1.9≦y≦2.1, and z=0 or

(c) 0.7≦x≦0.9, 2.1≦y≦2.3, and z=0

are especially preferred because they bring about a satisfactory balanceamong battery performances.

Especially preferred typical compositions of those compounds are:Li_(4/3)Ti_(5/3)O₄ for (a), Li₁Ti₂O₄ for (b), and Li_(4/5)Ti_(11/5)O₄for (c). Preferred examples of the structure wherein z≠0 includeLi_(4/3)Ti_(4/3)Al_(1/3)O₄.

It is preferred that the lithium-titanium composite oxide for use as thenegative-electrode active material in the invention should satisfy atleast one of the following features (1) to (13) concerning properties,shape, etc., besides the requirements described above. Especiallypreferably, the composite oxide simultaneously satisfies two or more ofthe following features.

(1) BET Specific Surface Area

The BET specific surface area of the lithium-titanium composite oxidefor use as the negative-electrode active material, as determined by theBET method, is preferably 0.5 m²·g⁻¹ or larger, more preferably 0.7m²·g⁻¹ or larger, even more preferably 1.0 m²·g⁻¹ or larger, especiallypreferably 1.5 m²·g⁻¹ or larger, and is preferably 200 m²·g⁻¹ orsmaller, more preferably 100 m²·g⁻¹ or smaller, even more preferably 50m²·g⁻¹ or smaller, especially preferably 25 m²·g¹ or smaller. When theBET specific surface area thereof is smaller than the lower limit ofthat range, there are cases where use of this composite oxide as anegative-electrode material results in a reduced reaction area availablefor contact with the nonaqueous electrolyte and in an increase in outputresistance. On the other hand, in case where the BET specific surfacearea thereof exceeds the upper limit of that range, the proportion ofsurfaces and edge faces of crystals of the titanium-containing metaloxide increases and this causes crystal deformation. There are hencecases where irreversible capacity becomes not negligible and a preferredbattery is difficult to obtain.

BET specific surface area is determined with a surface area meter (afully automatic surface area measuring apparatus manufactured by OhukuraRiken Co., Ltd.) by preliminarily drying a sample at 350° C. for 15minutes in a nitrogen stream and then measuring the specific surfacearea thereof by the gas-flowing nitrogen adsorption BET one-point methodusing a nitrogen/helium mixture gas precisely regulated so as to have anitrogen pressure of 0.3 relative to atmosphere pressure. The specificsurface area determined through this measurement is defined as the BETspecific surface area of the lithium-titanium composite oxide in theinvention.

(2) Volume-Average Particle Diameter

The volume-average particle diameter (secondary-particle diameter in thecase where the primary particles have aggregated to form secondaryparticles) of the lithium-titanium composite oxide is defined as thevolume-average particle diameter (median diameter) determined by thelaser diffraction/scattering method.

The volume-average particle diameter of the lithium-titanium compositeoxide is generally 0.1 μm or larger, preferably 0.5 μm or larger, morepreferably 0.7 μm or larger, and is generally 50 μm or smaller,preferably 40 μm or smaller, even more preferably 30 μm or smaller,especially preferably 25 μm or smaller.

Volume-average particle diameter is determined by dispersing thelithium-titanium composite oxide in a 0.2% by mass aqueous solution(about 10 mL) of poly(oxyethylene(20)) sorbitan monolaurate as asurfactant and examining the dispersion with a laserdiffraction/scattering type particle size distribution analyzer (LA-700,manufactured by HORIBA, Ltd.). The median diameter determined by thismeasurement is defined as the volume-average particle diameter of thecarbonaceous material in the invention.

When the volume-average particle diameter of the lithium-titaniumcomposite oxide is smaller than the lower limit of that range, there arecases where a large amount of a binder is necessary in electrodeproduction and this results in a decrease in battery capacity. When thevolume-average particle diameter thereof exceeds the upper limit of thatrange, there are cases where such a composite oxide is undesirable fromthe standpoint of battery production because an uneven coating surfaceis apt to result when an electrode plate is produced.

(3) Average Primary-Particle Diameter

In the case where the primary particles have aggregated to formsecondary particles, the average primary-particle diameter of thelithium-titanium composite oxide is generally 0.01 μm or larger,preferably 0.05 μm or larger, more preferably 0.1 μm or larger,especially preferably 0.2 μm or larger, and is generally 2 μm orsmaller, preferably 1.6 μm or smaller, more preferably 1.3 μm orsmaller, especially preferably 1 μm or smaller. In case where thevolume-average primary-particle diameter thereof exceeds the upper limitof that range, spherical secondary particles are difficult to form andthis adversely influences powder loading or results in a considerablyreduced specific surface area. There may hence be a high possibilitythat battery performances such as output characteristics might decrease.When the average primary-particle diameter thereof is smaller than thelower limit of that range, crystal growth is usually insufficient and,hence, there are cases where use of this composite oxide gives asecondary battery having reduced performances, e.g., poorcharge/discharge reversibility.

Primary-particle diameter is determined through an examination with ascanning electron microscope (SEM). Specifically, arbitrarily selected50 primary-particle images in a photograph having a magnificationcapable of particle observation, e.g., 10,000-100,000 diameters, eachare examined for the length of the longest segment of a horizontal linewhich extends across the primary-particle image from one side to theother side of the boundary. These measured lengths are averaged, wherebythe average value can be determined.

(4) Shape

The shape of the particles of the lithium-titanium composite oxide maybe any of massive, polyhedral, spherical, ellipsoidal, platy, acicular,columnar, and other shapes such as those in common use. Preferred ofthese is one in which the primary particles have aggregated to formsecondary particles and these secondary particles have a spherical orellipsoidal shape.

In electrochemical elements, the active material in each electrodeusually expands/contracts with the charge/discharge of the element and,hence, deterioration is apt to occur, such as active-material breakageand conduction path breakage, due to the stress caused by theexpansion/contraction. Because of this, an active material in which theprimary particles have aggregated to form secondary particles ispreferable to an active material composed of primary particles onlysince the particles in the former active material relieve the stresscaused by expansion/contraction to prevent deterioration.

Furthermore, particles of a spherical or ellipsoidal shape arepreferable to particles showing axial orientation, e.g., platy ones,because the former particles are less apt to orient during electrodemolding and hence this electrode is reduced in expansion/contractionduring charge/discharge, and because these particles are apt to beevenly mixed with a conductive material in electrode production.

(5) Tap Density

The tap density of the lithium-titanium composite oxide is preferably0.05 g·cm⁻³ or higher, more preferably 0.1 g·cm⁻³ or higher, even morepreferably 0.2 g·cm⁻³ or higher, especially preferably 0.4 g·cm⁻³ orhigher, and is preferably 2.8 g·cm⁻³ or lower, more preferably 2.4g·cm⁻³ or lower, especially preferably 2 g·cm⁻³ or lower. In case wherethe tap density thereof is lower than the lower limit of that range,this composite oxide, when used in a negative electrode, is less apt tohave a high loading density and has a reduced interparticle contactarea. There are hence cases where interparticle resistance increases andoutput resistance increases. On the other hand, in case where the tapdensity thereof exceeds the upper limit of that range, the electrode hastoo small an amount of interparticle interstices and a reduced amount ofchannels for the nonaqueous electrolyte. There are hence cases whereoutput resistance increases.

The tap density of a sample is determined by dropping the sample througha sieve having an opening size of 300 μm into a 20 cm³ tapping cell tofill the cell with the sample up to the brim, subsequently conductingtapping operations 1,000 times over a stroke length of 10 mm using apowder densimeter (e.g., Tap Denser, manufactured by Seishin EnterpriseCo., Ltd.), and calculating a density from the resultant volume of thesample and the weight thereof. The tap density calculated through thismeasurement is defined as the tap density of the lithium-titaniumcomposite oxide in the invention.

(6) Roundness

When the lithium-titanium composite oxide is examined for roundness asan index to the degree of sphericity thereof, the roundness thereof ispreferably within the range shown below. Roundness is defined by“Roundness=(length of periphery of equivalent circle having the samearea as projected particle shape)/(actual length of periphery ofprojected particle shape)”. When a particle has a roundness of 1, thisparticle theoretically is a true sphere.

The closer to 1 the roundness of the lithium-titanium composite oxide,the more the particles thereof are desirable. The roundness of thecomposite oxide is generally 0.10 or higher, preferably 0.80 or higher,more preferably 0.85 or higher, especially preferably 0.90 or higher.The higher the roundness, the more the high-current-densitycharge/discharge characteristics are improved. Consequently, when theroundness of the composite oxide is lower than the lower limit of thatrange, there are cases where the negative-electrode active material hasreduced suitability for loading and interparticle resistance isincreased, resulting in reduced short-time high-current-densitycharge/discharge characteristics.

Roundness is determined with a flow type particle image analyzer (FPIA,manufactured by Sysmex Industrial Corp.). About 0.2 g of a sample isdispersed in a 0.2% by mass aqueous solution (about 50 mL) ofpoly(oxyethylene(20)) sorbitan monolaurate as a surfactant, and anultrasonic wave of 28 kHz is propagated to the dispersion for 1 minuteat an output of 60 W. Thereafter, particles having a particle diameterin the range of 3-40 μm are examined with the analyzer having adetection range set at 0.6-400 μm. The roundness determined through thismeasurement is defined as the roundness of the lithium-titaniumcomposite oxide in the invention.

(7) Aspect Ratio

The aspect ratio of the lithium-titanium composite oxide is generally 1or higher, and is generally 5 or lower, preferably 4 or lower, morepreferably 3 or lower, especially preferably 2 or lower. When the aspectratio thereof exceeds the upper limit of that range, there are caseswhere this composite oxide causes streak lines in electrode plateformation and an even coating surface cannot be obtained, resulting in adecrease in short-time high-current-density charge/dischargecharacteristics. Incidentally, the lower limit of that range is atheoretical lower limit of the aspect ratio of lithium-titaniumcomposite oxides.

In determining aspect ratio, particles of the lithium-titanium compositeoxide are examined with a scanning electron microscope with enlargement.Fifty are arbitrarily selected from composite-oxide particles fixed toan edge face of a metal having a thickness of 50 μm or smaller, and eachparticle is examined in a three-dimensional manner while rotating orinclining the stage to which the sample is fixed. In this examination,the length of the longest axis A of each particle and the length of theshortest axis B perpendicular to that axis are measured, and the averageof the A/B values is determined. The aspect ratio (A/B) determinedthrough this measurement is defined as the aspect ratio of thelithium-titanium composite oxide in the invention.

(8) Processes for Producing Negative-Electrode Active Material

Processes for producing the lithium-titanium composite oxide are notparticularly limited unless they depart from the spirit of theinvention. Examples thereof include several processes, and processes ingeneral use for producing inorganic compounds may be employed.

Examples thereof include a method in which a titanium source, e.g.,titanium oxide, is evenly mixed with a lithium source, e.g., LiOH, Li₂CO₃, or LiNO₃, and optionally with a source of other element(s) and thismixture is burned at a high temperature to obtain the active material.

Especially for producing spherical or ellipsoidal active materials,various techniques are usable. Examples thereof include: a method whichcomprises dissolving or pulverizing/dispersing a titanium source, e.g.,titanium oxide, optionally together with a source of other element(s) ina solvent, e.g., water, regulating the pH of the solution or dispersionwith stirring to produce a spherical precursor, recovering andoptionally drying the precursor, subsequently adding thereto a lithiumsource, e.g., LiOH, Li₂ CO₃, or LiNO₃, and burning the mixture at a hightemperature to obtain the active material.

Another example is a method which comprises dissolving orpulverizing/dispersing a titanium source, e.g., titanium oxide,optionally together with a source of other element(s) in a solvent,e.g., water, drying and forming the solution or dispersion with a spraydryer or the like to obtain a spherical or ellipsoidal precursor, addingthereto a lithium source, e.g., LiOH, Li₂ CO₃, or LiNO₃, and burning themixture at a high temperature to obtain the active material.

Still another example is a method which comprises dissolving orpulverizing/dispersing a titanium source, e.g., titanium oxide, togetherwith a lithium source, e.g., LiOH, Li₂ CO₃, or LiNO₃, and optionallywith a source of other element(s) in a solvent, e.g., water, drying andforming the solution or dispersion with a spray dryer or the like toobtain a spherical or ellipsoidal precursor, and burning the precursorat a high temperature to obtain the active material.

In those steps, one or more of elements other than Ti, such as, e.g.,Al, Mn, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, C, Si, Sn,and Ag, can be caused to be present in the titanium-containing metaloxide structure and/or present so as be in contact with thetitanium-containing oxide. The incorporation of such elements can beused for regulating the operating voltage and capacity of the battery.

(9) Electrode Production

Any known method can be used for electrode production. For example, abinder and a solvent are added to a negative-electrode active materialoptionally together with a thickener, conductive material, filler, etc.to obtain a slurry and this slurry is applied to a current collector anddried. Thereafter, the coated current collector is pressed, whereby anelectrode can be formed.

The thickness of the negative-electrode active-material layer per oneside in the stage just before the step of injecting a nonaqueouselectrolyte in battery fabrication is generally 15 μm or larger,preferably 20 μm or larger, more preferably 30 μm or larger. The upperlimit thereof desirably is 150 μm or smaller, preferably 120 μm orsmaller, more preferably 100 μm or smaller. When the thickness thereofis larger than the upper limit of that range, a nonaqueous electrolyteis less apt to infiltrate into around the interface of the currentcollector and, hence, there are cases where high-current-densitycharge/discharge characteristics decrease. When the thickness thereof issmaller than the lower limit of that range, the proportion by volume ofthe current collector to the negative-electrode active materialincreases and there are cases where battery capacity decreases. Thenegative-electrode active material may be roller-pressed to obtain asheet electrode, or may be subjected to compression molding to obtain apellet electrode.

(10) Current Collector

As the current collector for holding the negative-electrode activematerial, a known one can be used at will. Examples of the currentcollector for the negative electrode include metallic materials such ascopper, nickel, stainless steel, and nickel-plated steel. Copper isespecially preferred of these from the standpoints of processability andcost.

In the case where the current collector is a metallic material, examplesof the shape of the current collector include metal foils, metalcylinders, metal coils, metal plates, thin metal films, expanded metals,punching metals, and metal foams. Preferred of these are metal foilfilms including copper (Cu) and/or aluminum (Al). More preferred arecopper foils and aluminum foils. Even more preferred are a rolled copperfoil, which is produced by the rolling process, and an electrolyticcopper foil, which is produced by the electrolytic process. Either ofthese can be used as a current collector.

In the case of a copper foil having a thickness smaller than 25 μm, usecan be made of a copper alloy (e.g., phosphor bronze, titanium-copper,Corson alloy, or Cu—Cr—Zr alloy) having a higher strength than purecopper. Furthermore, an aluminum foil can be advantageously used becauseit has a low specific gravity and, hence, use of the foil as a currentcollector can reduce the weight of the battery.

The current collector comprising a copper foil produced by the rollingprocess is less apt to crack even when the negative electrode is rolledtightly or rolled at an acute angle, because the copper crystals areoriented in the rolling direction. This current collector can beadvantageously used in small cylindrical batteries.

The electrolytic copper foil is obtained by immersing a metallic drum ina nonaqueous electrolyte containing copper ions dissolved therein,causing current to flow through the system while rotating the drum tothereby deposit copper on the drum surface, and peeling the copperdeposit from the drum. Copper may be deposited on a surface of therolled copper foil by the electrolytic process. One or each side of sucha copper foil may have undergone a surface-roughening treatment or asurface treatment (e.g., a chromate treatment in a thickness of fromseveral nanometers to about 1 μm or a priming treatment with titanium).

The current collector base is desired to further have the followingproperties.

(10-1) Average Surface Roughness (Ra)

The average surface roughness (Ra) of that side of the current collectorbase on which a thin active-material film is to be formed, as determinedby the method provided for in JIS B 0601-1994, is not particularlylimited. However, the average surface roughness thereof is generally0.01 μm or higher, preferably 0.03 μm or higher, and is generally 1.5 μmor lower, preferably 1.3 μm or lower, more preferably 1.0 μm or lower.

This is because when the average surface roughness (Ra) of the currentcollector base is within that range, satisfactory charge/discharge cyclecharacteristics can be expected. In addition, the area of the interfacebetween the base and a thin active-material film is increased andadhesion to the thin negative-electrode active-material film isimproved. The upper limit of the average surface roughness (Ra) thereofis not particularly limited. However, a current collector base having anaverage surface roughness (Ra) of 1.5 μm or lower is usually employedbecause a foil having a practical thickness for batteries and having anRa exceeding 1.5 μm is generally difficult to procure.

(10-2) Tensile Strength

Tensile strength is a quotient obtained by dividing the maximum tensileforce required before test piece breakage by the sectional area of thetest piece. In the invention, the tensile strength is determined througha measurement conducted with the same apparatus and by the same methodas those described in JIS Z 2241 (Method of Metallic-Material TensileTest).

The tensile strength of the current collector base is not particularlylimited. However, it is generally 50 N·mm⁻² or higher, preferably 100N·mm⁻² or higher, more preferably 150 N·mm⁻² or higher. The higher thetensile strength, the more the current collector base is preferred.However, it is desirable that the tensile strength thereof should begenerally 1,000 N·mm⁻² or lower from the standpoint of industrialavailability. A current collector base having a high tensile strengthcan be inhibited from cracking with the expansion/contraction of thethin active-material film which occur upon charge/discharge. With thiscurrent collector base, satisfactory cycle characteristics can beobtained.

(10-3) 0.2% Proof Stress

The term 0.2% proof stress means the degree of load necessary forimparting a plastic (permanent) deformation of 0.2%. Namely, it meansthat application of that degree of load and subsequent removal thereofresult in a 0.2% deformation. The 0.2% proof stress is determinedthrough a measurement conducted with the same apparatus and by the samemethod as for tensile strength.

The 0.2% proof stress of the current collector base is not particularlylimited. However, the 0.2% proof stress thereof is generally 30 N·mm⁻²or higher, preferably 100 N·mm⁻² or higher, especially preferably 150N/mm² or higher. The higher the 0.2% proof stress, the more the currentcollector base is preferred. However, the 0.2% proof stress thereof isgenerally desirably 900 N·mm⁻² or lower from the standpoint ofindustrial availability. A current collector base having a high 0.2%proof stress can be inhibited from plastically deforming with theexpansion/contraction of the thin active-material film which occur uponcharge/discharge. With this current collector base, satisfactory cyclecharacteristics can be obtained.

(10-4) Thickness of Current Collector

The current collector may have any desired thickness. However, thethickness thereof is generally 1 μl or larger, preferably 3 μm orlarger, more preferably 5 μm or larger, and is generally 1 mm orsmaller, preferably 100 μm or smaller, more preferably 50 μm or smaller.In case where the current collector is thinner than 1 μm, this collectorhas reduced strength and there are hence cases where coating isdifficult. When the current collector is thicker than 100 μl, there arecases where this collector deforms an electrode shape, e.g., a rolledform. The current collector may be in a mesh form.

(11) Thickness Ratio Between Current Collector and Active-Material Layer

The thickness ratio between the current collector and theactive-material layer is not particularly limited. However, the value of“(thickness of the active-material layer on one side just beforeimpregnation with the nonaqueous electrolyte)/(thickness of the currentcollector)” is generally 150 or smaller, preferably 20 or smaller, morepreferably 10 or smaller, and is generally 0.1 or larger, preferably 0.4or larger, more preferably 1 or larger. When the thickness ratio betweenthe current collector and the negative-electrode active-material layerexceeds the upper limit of that range, there are cases where thiscurrent collector heats up due to Joule's heat duringhigh-current-density charge/discharge. When that ratio decreases beyondthe lower limit of that range, the proportion by volume of the currentcollector to the negative-electrode active material increases and thismay reduce the capacity of the battery.

(12) Electrode Density

When the negative-electrode active material is used to form anelectrode, the electrode structure is not particularly limited. However,the density of the active material present on the current collector ispreferably 1.0 g·cm⁻³ or higher, more preferably 1.2 g·cm⁻³ or higher,even more preferably 1.3 g·cm⁻³ or higher, especially preferably 1.5g·cm⁻³ or higher, and is preferably 3 g·cm⁻³ or lower, more preferably2.5 g·cm⁻³ or lower, even more preferably 2.2 g·cm⁻³ or lower,especially preferably 2 g·cm⁻³ or lower. When the density of the activematerial present on the current collector exceeds the upper limit ofthat range, there are cases where bonding between the current collectorand the negative-electrode active material is weak and the activematerial sheds from the electrode. When the density thereof is lowerthan the lower limit of that range, there are cases where electricalconductivity among particles of the negative-electrode active materialdecreases and this increases battery resistance.

(13) Binder

The binder for binding the negative-electrode active material is notparticularly limited so long as it is stable to the nonaqueouselectrolyte and to the solvent to be used for electrode production.

Examples thereof include resinous polymers such as polyethylene,polypropylene, poly(ethylene terephthalate), poly(methyl methacrylate),polyimides, aromatic polyamides, cellulose, and nitrocellulose; rubberypolymers such as SBR (styrene/butadiene rubbers), isoprene rubbers,butadiene rubbers, fluororubbers, NBR (acrylonitrile/butadiene rubbers),and ethylene/propylene rubbers; styrene/butadiene/styrene blockcopolymers or products of hydrogenation thereof; thermoplasticelastomeric polymers such as EPDM (ethylene/propylene/dieneterpolymers), styrene/ethylene/butadiene/styrene copolymers, andstyrene/isoprene/styrene block copolymers and products of hydrogenationthereof; flexible resinous polymers such assyndiotactic-1,2-polybutadiene, poly(vinyl acetate), ethylene/vinylacetate copolymers, and propylene/α-olefin copolymers; fluorochemicalpolymers such as poly(vinylidene fluoride), polytetrafluoroethylene,fluorinated poly(vinylidene fluoride), andpolytetrafluoroethylene/ethylene copolymers; and polymer compositionshaving the property of conducting alkali metal ions (especially lithiumions). One of these may be used alone, or any desired combination of twoor more thereof in any desired proportion may be used.

The kind of the solvent to be used for forming a slurry is notparticularly limited so long as it is a solvent in which thenegative-electrode active material and binder and the thickener andconductive material which are optionally used according to need can bedissolved or dispersed. Either an aqueous solvent or an organic solventmay be used.

Examples of the aqueous solvent include water and alcohols. Examples ofthe organic solvent include N-methylpyrrolidone (NMP),dimethylformamide, dimethylacetamide, methyl ethyl ketone,cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine,N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone,diethyl ether, dimethylacetamide, hexamethylphosphoramide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, andhexane. Especially when an aqueous solvent is used, a dispersant or thelike is added in combination with the thickener described above toprepare a slurry using a latex of, e.g., SBR. One of such ingredientsmay be used alone, or any desired combination of two or more thereof inany desired proportion may be used.

The proportion of the binder to the negative-electrode active materialis generally 0.1% by mass or higher, preferably 0.5% by mass or higher,more preferably 0.6% by mass or higher, and is generally 20% by mass orlower, preferably 15% by mass or lower, more preferably 10% by mass orlower, especially preferably 8% by mass or lower. In case where theproportion of the binder to the negative-electrode active materialexceeds the upper limit of that range, the proportion of the binderwhich does not contribute to battery capacity increases and this maylead to a decrease in battery capacity. When the binder proportion issmall than the lower limit, there are cases where the negative electrodehas reduced strength and this is undesirable from the standpoint ofbattery fabrication step.

Especially when the binder includes a rubbery polymer represented by SBRas the main component, the proportion of this binder to the activematerial is generally 0.1% by mass or higher, preferably 0.5% by mass orhigher, more preferably 0.6% by mass or higher, and is generally 5% bymass or lower, preferably 3% by mass or lower, more preferably 2% bymass or lower.

In the case where the binder includes a fluorochemical polymerrepresented by poly(vinylidene fluoride) as the main component, theproportion of this binder to the active material is 1% by mass orhigher, preferably 2% by mass or higher, more preferably 3% by mass orhigher, and is generally 15% by mass or lower, preferably 10% by mass orlower, more preferably 8% by mass or lower.

A thickener is used generally for the purpose of regulating the slurryviscosity. The thickener is not particularly limited. Examples thereofinclude carboxymethyl cellulose, methyl cellulose, hydroxymethylcellulose, ethyl cellulose, poly(vinyl alcohol), oxidized starch,phosphorylated starch, casein, and salts of these. One of thesethickeners may be used alone, or any desired combination of two or morethereof in any desired proportion may be used.

In the case where such a thickener is further added, the proportion ofthe thickener to the negative-electrode active material is generally0.1% by mass or higher, preferably 0.5% by mass or higher, morepreferably 0.6% by mass or higher, and is generally 5% by mass or lower,preferably 3% by mass or lower, more preferably 2% by mass or lower.When the proportion thereof is lower than the lower limit of that range,there are cases where applicability decreases considerably. Proportionsthereof exceeding the upper limit of that range result in a reducedproportion of the active material in the negative-electrodeactive-material layer, and this may pose a problem that battery capacitydecreases and a problem that resistance among the particles of thenegative-electrode active material increases.

<2-4. Positive Electrode>

The positive electrode for use in the nonaqueous-electrolyte secondarybattery of this invention is explained below.

<2-4-1. Positive-Electrode Active Material>

Positive-electrode active materials usable in the positive electrode areexplained below.

(1) Composition

The positive-electrode active materials are not particularly limited solong as these are capable of electrochemically occluding/releasinglithium ions. For example, however, a substance containing lithium andat least one transition metal is preferred. Examples thereof includelithium-transition metal composite oxides and lithium-containingtransition metal/phosphoric acid compounds.

The transition metal in the lithium-transition metal composite oxidespreferably is V, Ti, Cr, Mn, Fe, Co, Ni, Cu, or the like. Specificexamples of the composite oxides include lithium-cobalt composite oxidessuch as LiCoO₂, lithium-nickel composite oxides such as LiNiO₂,lithium-manganese composite oxides such as LiMnO₂, LiMn₂O₄, and Li₂MnO₄,and ones formed by partly replacing the transition metal atom(s) as amain component of these lithium-transition metal composite oxides by oneor more other metals, e.g., Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn,Mg, Ga, Zr, Si, etc.

Examples of such compounds formed by replacement includeLiNi_(0.5)Mn_(0.5)O₂, LiNi_(0.85)Co_(0.10)Al_(0.05)O₂,LiNi_(0.33)CO_(0.33)Mn_(0.33)O₂, LiMn_(1.8)Al_(0.2)O₄, andLiMn_(1.5)Ni_(0.5)O₄, etc.

The transition metal in the lithium-containing transitionmetal/phosphoric acid compounds preferably is V, Ti, Cr, Mn, Fe, Co, Ni,Cu, or the like. Specific examples of the compounds include ironphosphate compounds such as LiFePO₄, Li₃Fe₂ (PO₄)₃ and LiFeP₂O₇, cobaltphosphate compounds such as LiCoPO₄, and ones formed by partly replacingthe transition metal atom(s) as a main component of theselithium-transition metal/phosphoric acid compounds by one or more othermetals, e.g., Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb,Si, etc.

(2) Surface Coating

Use may be made of a material including any of those positive-electrodeactive materials and, adherent to the surface thereof, a substance(hereinafter abbreviated to “surface-adherent substance”) having acomposition different from that of the substance constituting the corepositive-electrode active material. Examples of the surface-adherentsubstance include oxides such as aluminum oxide, silicon oxide, titaniumoxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide,antimony oxide, and bismuth oxide, sulfates such as lithium sulfate,sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate,and aluminum sulfate, and carbonates such as lithium carbonate, calciumcarbonate, and magnesium carbonate and the like.

Those surface-adherent substances each can be adhered to the surface ofa positive-electrode active material, for example, by: a method in whichthe substance is dissolved or suspended in a solvent and this solutionor suspension is infiltrated into a positive-electrode active materialand then dried; a method in which a precursor for the surface-adherentsubstance is dissolved or suspended in a solvent and this solution orsuspension is infiltrated into a positive-electrode active material andthen heated or otherwise treated to react the precursor; or a method inwhich the substance is added to a precursor for a positive-electrodeactive material and heat-treated together with the precursor.

The mass of the surface-adherent substance adherent to the surface ofthe positive-electrode active material is generally 0.1 ppm or larger,preferably 1 ppm or larger, more preferably 10 ppm or larger, in termsof mass ppm of the positive-electrode active material. The amountthereof is generally 200 or smaller, preferably 10% or smaller, morepreferably 5% or smaller, based on the mass of the positive-electrodeactive material.

The surface-adherent substance serves to inhibit the nonaqueouselectrolyte from undergoing an oxidation reaction on the surface of thepositive-electrode active material, whereby the battery life can beimproved. However, in case where the amount of the substance adhered issmaller than the lower limit of that range, that effect is notsufficiently produced. On the other hand, amounts thereof exceeding theupper limit of that range may result in an increase in resistancebecause the surface-adherent substance inhibits the occlusion/release oflithium ions. Consequently, that range is preferred.

(3) Shape

The shape of the particles of the positive-electrode active material maybe any of massive, polyhedral, spherical, ellipsoidal, platy, acicular,columnar, and other shapes such as those in common use. Preferred ofthese is one in which the primary particles have aggregated to formsecondary particles and these secondary particles have a spherical orellipsoidal shape.

The reasons for that are as follows. In electrochemical elements, theactive material in each electrode usually expands/contracts with thecharge/discharge of the element and, hence, deterioration is apt tooccur, such as active-material breakage and conduction path breakage,due to the stress caused by the expansion/contraction. Consequently, apositive-electrode active material in which the primary particles haveaggregated to form secondary particles is preferable to an activematerial composed of primary particles only since the particles in theformer active material relieve the stress caused byexpansion/contraction to prevent deterioration.

Furthermore, particles of a spherical or ellipsoidal shape arepreferable to particles showing axial orientation, e.g., platy ones,because the former particles are less apt to orient during electrodemolding and hence this electrode is reduced in expansion/contractionduring charge/discharge, and because these particles are apt to beevenly mixed with a conductive material in electrode production.

(4) Tap Density

The tap density of the positive-electrode active material is generally1.3 g·cm⁻³ or higher, preferably 1.5 g·cm⁻³ or higher, more preferably1.6 g·cm⁻³ or higher, especially preferably 1.7 g·cm⁻³ or higher, and isgenerally 2.5 g·cm⁻³ or lower, preferably 2.4 g·cm⁻³ or lower.

By using a metal composite oxide powder having a high tap density, apositive-electrode active-material layer having a high density can beformed. Consequently, when the tap density of the positive-electrodeactive material is lower than the lower limit of that range, not only itis necessary to use a larger amount of a dispersion medium and largeramounts of a conductive material and a binder in forming apositive-electrode active-material layer. There are hence cases wherethe loading of the positive-electrode active material in thepositive-electrode active-material layer is limited, resulting in alimited battery capacity. The higher the tap density, the more thepositive-electrode active material is generally preferred. There is noparticular upper limit on the tap density. However, when the tap densitythereof is lower than that range, there are cases where the diffusion oflithium ions in the positive-electrode active-material layer through thenonaqueous electrolyte as a medium becomes a rate-determining stage andthis is apt to reduce load characteristics.

The tap density of a sample is determined by dropping the sample througha sieve having an opening size of 300 μm into a 20 cm³ tapping cell tofill the capacity of the cell with the sample, subsequently conductingtapping operations 1,000 times over a stroke length of 10 mm using apowder densimeter (e.g., Tap Denser, manufactured by Seishin EnterpriseCo., Ltd.), and determining a density from the resultant volume of thesample and the weight thereof. The tap density determined through thismeasurement is defined as the tap density of the positive-electrodeactive material in the invention.

(5) Median Diameter d50

The median diameter d50 (secondary-particle diameter in the case wherethe primary particles have aggregated to form secondary particles) ofthe particles of the positive-electrode active material can bedetermined also with a laser diffraction/scattering type particle sizedistribution analyzer.

The median diameter d50 thereof is generally 0.1 or larger, preferably0.5 μm or larger, more preferably 1 μm or larger, especially preferably3 μm or larger, and is generally 20 μm or smaller, preferably 18 μm orsmaller, more preferably 16 μm or smaller, especially preferably 15 μmor smaller. When the median diameter d50 thereof is smaller than thelower limit of that range, there are cases where a product having a highbulk density cannot be obtained. When the median diameter thereofexceeds the upper limit of that range, lithium diffusion in theindividual particles requires a longer time and this results in adecrease in battery performance. In addition, there are cases where suchpositive-electrode active-material particles, when used in producing apositive electrode for batteries, i.e., when the active material andother ingredients including a conductive material and a binder areslurried with a solvent and this slurry is applied in a thin-film form,pose a problem, for example, that streak lines generate.

It is possible to further improve loading in positive-electrodeproduction by mixing two or more positive-electrode active materialsdiffering in median diameter d50.

In determining median diameter d50, a 0.1% by mass aqueous solution ofsodium hexametaphosphate is used as a dispersion medium. LA-920,manufactured by HORIBA, Ltd., is used as a particle size distributionanalyzer to conduct a five-minute ultrasonic dispersing treatment,before the particles are examined at a measuring refractive index set at1.24.

(6) Average Primary-Particle Diameter

In the case where the primary particles have aggregated to formsecondary particles, the average primary-particle diameter of thispositive-electrode active material is generally 0.01 μm or larger,preferably 0.05 μm or larger, more preferably 0.08 μm or larger,especially preferably 0.1 μm or larger, and is generally 3 μm orsmaller, preferably 2 μm or smaller, more preferably 1 μm or smaller,especially preferably 0.6 μm or smaller. The reasons for this are asfollows. In case where the average primary-particle diameter thereofexceeds the upper limit of that range, spherical secondary particles aredifficult to form and this adversely influences powder loading orresults in a considerably reduced specific surface area. There may hencebe a high possibility that battery performances such as outputcharacteristics might decrease. When the average primary-particlediameter thereof is smaller than the lower limit of that range, crystalgrowth is usually insufficient and, hence, there are cases where use ofthis positive-electrode active material gives a secondary battery havingreduced performances, e.g., poor charge/discharge reversibility.

Average primary-particle diameter is determined through an examinationwith a scanning electron microscope (SEM). Specifically, arbitrarilyselected 50 primary-particle images in a photograph having amagnification of 10,000 diameters each are examined for the length ofthe longest segment of a horizontal line which extends across theprimary-particle image from one side to the other side of the boundary.These measured lengths are averaged, whereby the average value can bedetermined.

(7) BET Specific Surface Area

The BET specific surface area of the positive-electrode active material,in terms of the value of specific surface area as determined by the BETmethod, is generally 0.2 m²·g⁻¹ or larger, preferably 0.3 m²·g⁻¹ orlarger, more preferably 0.4 m²·g⁻¹ or larger, and is generally 4.0m²·g⁻¹ or smaller, preferably 2.5 m²·g⁻¹ or smaller, more preferably 1.5m²·g⁻¹ or smaller. In case where the BET specific surface area thereofis smaller than the lower limit of that range, battery performances areapt to decrease. In case where the BET specific surface area thereofexceeds the upper limit of that range, a high tap density is difficultto obtain and there are cases where applicability in forming apositive-electrode active-material layer is poor.

BET specific surface area is measured with a surface area meter (a fullyautomatic surface area measuring apparatus manufactured by Ohukura RikenCo., Ltd.). The specific surface area is determined by preliminarilydrying a sample at 150° C. for 30 minutes in a nitrogen stream and thenmeasuring the specific surface area thereof by the gas-flowing nitrogenadsorption BET one-point method using a nitrogen/helium mixture gasprecisely regulated so as to have a nitrogen pressure of 0.3 relative toatmosphere pressure. The specific surface area determined through thismeasurement is defined as the BET specific surface area of thepositive-electrode active material in the invention.

(8) Processes for Producing Positive-Electrode Active Material

Processes for producing positive-electrode active materials are notparticularly limited unless the processes depart from the spirit of theinvention. Examples thereof include several processes. Techniques whichare in general use for producing inorganic compounds may be employed.

Especially for producing spherical or ellipsoidal active materials,various techniques are usable. Examples thereof include: a method whichcomprises dissolving or pulverizing/dispersing a transition metalsource, e.g., a transition metal nitrate or sulfate, optionally togetherwith a source of other element(s) in a solvent, e.g., water, regulatingthe pH of the solution or dispersion with stirring to produce aspherical precursor, recovering and optionally drying the precursor,subsequently adding thereto a lithium source, e.g., LiOH, Li₂ CO₃, orLiNO₃, and burning the mixture at a high temperature to obtain theactive material.

Another example is a method which comprises dissolving orpulverizing/dispersing a transition metal source, e.g., a transitionmetal nitrate, sulfate, hydroxide, or oxide, optionally together with asource of other element(s) in a solvent, e.g., water, drying and formingthe solution or dispersion with a spray dryer or the like to obtain aspherical or ellipsoidal precursor, adding thereto a lithium source,e.g., LiOH, Li₂ CO₃, or LiNO₃, and burning the mixture at a hightemperature to obtain the active material.

Still another example is a method which comprises dissolving orpulverizing/dispersing a transition metal source, e.g., a transitionmetal nitrate, sulfate, hydroxide, or oxide, together with a lithiumsource, e.g., LiOH, Li₂ CO₃, or LiNO₃, and optionally with a source ofother element(s) in a solvent, e.g., water, drying and forming thesolution or dispersion with a spray dryer or the like to obtain aspherical or ellipsoidal precursor, and burning the precursor at a hightemperature to obtain the active material.

<2-4-2. Electrode Structure and Production Process>

The constitution of the positive electrode to be used in this inventionand a process for producing the electrode will be described below.

(1) Process for Producing Positive Electrode

The positive electrode is produced by forming a positive-electrodeactive-material layer including particles of a positive-electrode activematerial and a binder on a current collector. The production of thepositive electrode with a positive-electrode active material can beconducted in an ordinary manner. Namely, a positive-electrode activematerial and a binder are mixed together by a dry process optionallytogether with a conductive material, thickener, etc. and this mixture isformed into a sheet and press-bonded to a positive-electrode currentcollector. Alternatively, those materials are dissolved or dispersed ina liquid medium to obtain a slurry and this slurry is applied to apositive-electrode current collector and dried. Thus, apositive-electrode active-material layer is formed on the currentcollector, whereby the positive electrode can be obtained.

The content of the positive-electrode active material in thepositive-electrode active-material layer is generally 10% by mass orhigher, preferably 30% by mass or higher, especially preferably 50% bymass or higher, and is generally 99.9% by mass or lower, preferably 99%by mass or lower. The reasons for this are as follows. When the contentof the positive-electrode active material in the positive-electrodeactive-material layer is lower than the lower limit of that range, thereare cases where an insufficient electrical capacity results. When thecontent thereof exceeds the upper limit of that range, there are caseswhere the positive electrode has insufficient strength. Onepositive-electrode active-material powder may be used alone in theinvention, or any desired combination of two or more positive-electrodeactive materials differing in composition or powder properties may beused in any desired proportion.

(2) Conductive Material

As the conductive material, a known conductive material can be used atwill. Examples thereof include metallic materials such as copper andnickel; graphites such as natural graphites and artificial graphites;carbon blacks such as acetylene black; and carbon materials such asamorphous carbon, e.g., needle coke. One of these materials may be usedalone, or any desired combination of two or more thereof in any desiredproportion may be used.

The conductive material may be used so that it is incorporated in thepositive-electrode active-material layer in an amount of generally 0.01%by mass or larger, preferably 0.1% by mass or larger, more preferably 1%by mass or larger, and of generally 50% by mass or lower, preferably 30%by mass or lower, more preferably 15% by mass or lower. When the contentthereof is lower than the lower limit of that range, there are caseswhere electrical conductivity becomes insufficient. Conversely, when thecontent thereof exceeds the upper limit of that range, there are caseswhere battery capacity decreases.

(3) Binder

The binder to be used for producing the positive-electrodeactive-material layer is not particularly limited so long as the binderis stable to the nonaqueous electrolyte and to the solvent to be usedfor electrode production.

In the case where the layer is to be formed through coating fluidapplication, any binder may be used so long as it is a material which issoluble or dispersible in the liquid medium for use in electrodeproduction. Examples thereof include resinous polymers such aspolyethylene, polypropylene, poly(ethylene terephthalate), poly(methylmethacrylate), aromatic polyamides, cellulose, and nitrocellulose;rubbery polymers such as SBR (styrene/butadiene rubbers), NBR(acrylonitrile/butadiene rubbers), fluororubbers, isoprene rubbers,butadiene rubbers, and ethylene/propylene rubbers; thermoplasticelastomeric polymers such as styrene/butadiene/styrene block copolymersor products of hydrogenation thereof, EPDM (ethylene/propylene/dieneterpolymers), styrene/ethylene/butadiene/ethylene copolymers, andstyrene/isoprene/styrene block copolymers or products of hydrogenationthereof; flexible resinous polymers such assyndiotactic-1,2-polybutadiene, poly(vinyl acetate), ethylene/vinylacetate copolymers, and propylene/α-olefin copolymers; fluorochemicalpolymers such as poly(vinylidene fluoride) (PVdF),polytetrafluoroethylene, fluorinated poly(vinylidene fluoride), andpolytetrafluoroethylene/ethylene copolymers; and polymer compositionshaving the property of conducting alkali metal ions (especially lithiumions). One of these substances may be used alone, or any desiredcombination of two or more thereof in any desired proportion may beused.

The proportion of the binder in the positive-electrode active-materiallayer is generally 0.1% by mass or higher, preferably 1% by mass orhigher, more preferably 3% by mass or higher, and is generally 80% bymass or lower, preferably 60% by mass or lower, more preferably 40% bymass or lower, especially preferably 10% by mass or lower. When theproportion of the binder is lower than the lower limit of that range,there are cases where the positive-electrode active material cannot besufficiently held and the positive electrode has insufficient mechanicalstrength to impair battery performances such as cycle characteristics.When the proportion thereof is higher than the upper limit of thatrange, there are cases where such high proportions lead to a decrease inbattery capacity or conductivity.

(4) Liquid Medium

The kind of the liquid medium to be used for forming a slurry is notparticularly limited so long as it is a solvent in which thepositive-electrode active material, conductive material, and binder anda thickener, which is used according to need, can be dissolved ordispersed. Either an aqueous solvent or an organic solvent may be used.

Examples of the aqueous medium include water and mixed solventsincluding an alcohol and water. Examples of the organic medium includealiphatic hydrocarbons such as hexane; aromatic hydrocarbons such asbenzene, toluene, xylene, and methylnaphthalene; heterocyclic compoundssuch as quinoline and pyridine; ketones such as acetone, methyl ethylketone, and cyclohexanone; esters such as methyl acetate and methylacrylate; amines such as diethylenetriamine andN,N-dimethylaminopropylamine; ethers such as diethyl ether andtetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP),dimethylformamide, and dimethylacetamide; and aprotic polar solventssuch as hexamethylphosphoramide and dimethyl sulfoxide. One of theseliquid media may be used alone, or any desired combination of two ormore thereof in any desired proportion may be used.

(5) Thickener

When an aqueous medium is used as a liquid medium for forming a slurry,it is preferred to use a thickener and a latex of, e.g., astyrene/butadiene rubber (SBR) to prepare a slurry. A thickener is usedgenerally for the purpose of regulating the viscosity of the slurry.

The thickener is not particularly limited unless it considerably lessensthe effects of the invention. Examples thereof include carboxymethylcellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose,poly(vinyl alcohol), oxidized starch, phosphorylated starch, casein, andsalts of these. One of these thickeners may be used alone, or anydesired combination of two or more thereof in any desired proportion maybe used.

In the case where such a thickener is further used, the proportion ofthe thickener to the active material desirably is generally 0.1% by massor higher, preferably 0.5% by mass or higher, more preferably 0.6% bymass or higher, and is generally 5% by mass or lower, preferably 3% bymass or lower, more preferably 2% by mass or lower. When the proportionthereof is lower than the lower limit of that range, there are caseswhere applicability decreases considerably. Proportions thereofexceeding the upper limit of that range result in a reduced proportionof the active material in the positive-electrode active-material layer,and this may pose a problem that battery capacity decreases and aproblem that resistance among the particles of the positive-electrodeactive material increases.

(6) Compaction

It is preferred that the positive-electrode active-material layerobtained by coating fluid application and drying should be compactedwith a handpress, roller press, or the like in order to heighten theloading density of the positive-electrode active material. The densityof the positive-electrode active-material layer is preferably 1 g·cm⁻³or higher, more preferably 1.5 g·cm⁻³ or higher, especially preferably 2g·cm⁻³ or higher. The upper limit thereof is preferably 4 g·cm⁻³ orlower, more preferably 3.5 g·cm⁻³ or lower, especially preferably 3g·cm⁻³ or lower. When the density of the positive-electrodeactive-material layer exceeds the upper limit of that range, theinfiltration of a nonaqueous electrolyte into around the currentcollector/active material interface becomes insufficient and there arecases where charge/discharge characteristics especially at a highcurrent density decrease. When the density thereof is lower than thelower limit of that range, there are cases where electrical conductivityamong the active-material particles decreases to increase batteryresistance.

(7) Current Collector

The material of the positive-electrode current collector is notparticularly limited, and a known one can be used at will. Examplesthereof include metallic materials such as aluminum, stainless steel,nickel-plated materials, titanium, and tantalum; and carbon materialssuch as carbon cloths and carbon papers. Of these, metallic materialsare preferred. Especially preferred is aluminum.

In the case of a metallic material, examples of the shape of the currentcollector include metal foils, metal cylinders, metal coils, metalplates, thin metal films, expanded metals, punching metals, and metalfoams. In the case of a carbon material, examples of the collector shapeinclude carbon plates, thin carbon films, and carbon cylinders. Ofthese, a thin metal film is preferred. The thin film may be in asuitable mesh form.

Although the current collector may have any desired thickness, thethickness thereof is generally 1 μm or larger, preferably 3 μm orlarger, more preferably 5 μm or larger, and is generally 1 mm orsmaller, preferably 100 μm or smaller, more preferably 50 μm or smaller.When the thin film is thinner than the lower limit of that range, thereare cases where this film is deficient in strength required of a currentcollector. When the thin film is thicker than the upper limit of thatrange, there are cases where this film has impaired handleability.

<2-5. Separator>

A separator is generally interposed between the positive electrode andthe negative electrode in order to prevent short-circuiting. In thiscase, the nonaqueous electrolyte of this invention are usuallyinfiltrated into the separator.

The material and shape of the separator are not particularly limited,and known separators can be employed at will unless the effects of theinvention are considerably lessened thereby. In particular, use may bemade of separators constituted of materials stable to the nonaqueouselectrolyte of the invention, such as resins, glass fibers, andinorganic materials. It is preferred to use a separator which is in theform of a porous sheet, nonwoven fabric, or the like and has excellentliquid retentivity.

As the material of the resinous or glass-fiber separators, use can bemade of, for example, polyolefins such as polyethylene andpolypropylene, polytetrafluoroethylene, polyethersulfones, glassfilters, and the like. Preferred of these are glass filters andpolyolefins. More preferred are polyolefins. One of these materials maybe used alone, or any desired combination of two or more thereof in anydesired proportion may be used.

The separator may have any desired thickness. However, the thicknessthereof is generally 1 μm or larger, preferably 5 μm or larger, morepreferably 10 μm or larger, and is generally 50 μm or smaller,preferably 40 μm or smaller, more preferably 30 μm or smaller. When theseparator is thinner than the lower limit of that range, there are caseswhere insulating properties and mechanical strength decrease. When theseparator is thicker than the upper limit of that range, there are caseswhere battery performances including rate characteristics decrease. Inaddition, there also are cases where use of such a separator gives anonaqueous-electrode secondary battery which as a whole has a reducedenergy density.

In the case where a porous material such as, e.g., a porous sheet or anonwoven fabric is used as the separator, this separator may have anydesired porosity. However, the porosity thereof is generally 20% orhigher, preferably 35% or higher, more preferably 45% or higher, and isgenerally 90% or lower, preferably 85% or lower, more preferably 75% orlower. In case where the porosity thereof is lower than the lower limitof that range, this separator tends to have increased film resistance,resulting in impaired rate characteristics. In case where the porositythereof is higher than the upper limit of that range, this separatortends to have reduced mechanical strength and reduced insulatingproperties.

The separator may have any desired average pore diameter. However, theaverage pore diameter thereof is generally 0.5 μm or smaller, preferably0.2 μm or smaller, and is generally 0.05 μm or larger. In case where theaverage pore diameter thereof exceeds the upper limit of that range,short-circuiting is apt to occur. When the average pore diameter thereofis smaller than the lower limit of that range, there are cases wherethis separator has increased film resistance, resulting in reduced ratecharacteristics.

On the other hand, examples of the inorganic materials which may be usedinclude oxides such as alumina and silicon dioxide, nitrides such asaluminum nitride and silicon nitride, and sulfates such as bariumsulfate and calcium sulfate. Such materials of a particulate shape orfibrous shape may be used.

With respect to form, a separator of a thin film form may be used, suchas a nonwoven fabric, woven fabric, or microporous film. Suitable onesof a thin film form have a pore diameter of 0.01-1 μm and a thickness of5-50 μm. Besides such a separator in an independent thin film form, usecan be made of a separator obtained by forming a composite porous layercontaining particles of the inorganic material with a resinous binder ona surface layer of the positive electrode and/or negative electrode.Examples of such separators include a porous layer formed by fixingalumina particles having a 90% particle diameter smaller than 1 μm witha fluororesin as a binder on both sides of the positive electrode.

<2-6. Battery Design>

[Electrode Group]

The electrode group may be either of: one having a multilayer structurein which the positive-electrode plate and negative-electrode platedescribed above have been superposed through the separator describedabove; and one having a wound structure in which the positive-electrodeplate and negative-electrode plate described above have been spirallywound through the separator described above. The proportion of thevolume of the electrode group to the internal volume of the battery(hereinafter referred to as electrode group proportion) is generally 40%or higher, preferably 50% or higher, and is generally 90% or lower,preferably 80% or lower. In case where the electrode group proportion islower than the lower limit of that range, a decrease in battery capacityresults. In case where the electrode group proportion exceeds the upperlimit of that range, this battery has a reduced space volume. There arehence cases where battery heating-up causes members to expand and aliquid component of the electrolyte to have a heightened vapor pressure,resulting in an increased internal pressure. This battery is reduced invarious characteristics including charge/discharge cycling performanceand high-temperature storability, and there are even cases where the gasrelease valve, which releases the gas from the internal pressure, works.

[Current Collector Structure]

The current collector structure is not particularly limited. However,for more effectively realizing the improvement in dischargecharacteristics which is brought about by the nonaqueous electrolyte ofthis invention, it is preferred to employ a structure reduced in theresistance of wiring parts and joint parts. In the case where internalresistance has been reduced in this manner, use of the nonaqueouselectrolyte of the invention produces its effects especiallysatisfactorily.

In the case of electrode groups assembled into the multilayer structuredescribed above, a structure obtained by bundling the metallic coreparts of respective electrode layers and welding the bundled parts to aterminal is suitable. When each electrode has a large area, this resultsin increased internal resistance. In this case, it is preferred todispose two or more terminals in each electrode to reduce theresistance. In the case of an electrode group having the wound structuredescribed above, two or more lead structures may be disposed on each ofthe positive electrode and negative electrode and bundled into aterminal, whereby internal resistance can be reduced.

[Case]

The material of the case is not particularly limited so long as it is asubstance stable to the nonaqueous electrolyte to be used. For example,use may be made of metals such as nickel-plated steel sheets, stainlesssteel, aluminum or aluminum alloys, and magnesium alloys or laminatedfilms constituted of a resin and an aluminum foil. From the standpointof weight reduction, it is preferred to use a metal which is aluminum oran aluminum alloy or a laminated film.

Examples of the case made of such a metal include one of a sealedstructure formed by fusion-bonding metallic members to each other bylaser welding, resistance welding, or ultrasonic welding and one of acaulked structure obtained by caulking members of the metal through aresinous gasket. Examples of the case made of the laminated film includeone of a sealed structure formed by thermally fusion-bonding resinlayers to each other. For the purpose of enhancing sealability, a resindifferent from the resin used in the laminated film may be interposedbetween the resin layers. Especially when resin layers are to bethermally fusion-bonded to each other through a current collectorterminal to produce a sealed structure, metal/resin bonding is necessaryand, hence, a resin having polar groups or a modified resin having polargroups introduced therein is suitable for use as the resin to beinterposed.

[Protective Element]

Examples of the protective element include a PTC (positive temperaturecoefficient), which increases in resistance upon abnormal heating-up orwhen an excessive current flows, a temperature fuse, a thermister, and avalve (current breaker valve) which breaks current flow through thecircuit in abnormal heating-up based on an abrupt increase in theinternal pressure or internal temperature of the battery. It ispreferred to select such a protective element which does not work underordinary high-current use conditions. From the standpoint of highoutput, it is preferred to employ a design which prevents abnormalheating-up and thermal run-away even without a protective element.

[Casing]

The nonaqueous-electrolyte secondary battery of this invention isusually fabricated by housing the nonaqueous electrolyte, negativeelectrode, positive electrode, separator, etc. in a casing. This casingis not limited, and a known one can be employed at will unless thisconsiderably lessens the effects of the invention.

The casing may be made of any desired material. For example, however,nickel-plated iron, stainless steel, aluminum or an alloy thereof,nickel, titanium, or the like is generally used.

The casing may have any desired shape. For example, the casing may beany of the cylindrical type, prismatic type, laminate type, coin type,large type, and the like.

When a carbonate having a halogen atom and a monofluorophosphate and/ordifluorophosphate are incorporated into a nonaqueous electrolyte andthis nonaqueous electrolyte is used to fabricate a nonaqueous-electrodesecondary battery, then this secondary battery can have improvedstorability in high-temperature environments. Details of the reasons forthis are unclear. However, it is presumed that the coexistence of acarbonate having a halogen atom with a monofluorophosphate and/ordifluorophosphate in the electrolyte contributes to an improvement inthe properties of a protective coating film in some way. Furthermore, itis presumed that use of the carbonate having a halogen atom as a solventimproves the oxidation resistance of the nonaqueous electrolyte andhence inhibits this electrolyte from reacting with thepositive-electrode active material. This nonaqueous electrolyte ispresumed to contribute to an improvement in storability.

<Nonaqueous Electrolyte 2 and Nonaqueous-Electrolyte Secondary Battery2>

[1. Nonaqueous Electrolyte 2 for Secondary Battery]

The nonaqueous electrolyte for use in nonaqueous-electrolyte secondarybattery 2 of the invention (hereinafter suitably referred to as“nonaqueous electrolyte 2 in the invention”) is a nonaqueous electrolytemainly comprising a nonaqueous solvent and an electrolyte dissolvedtherein, and is characterized by containing a compound which is liquidat 25° C., has a permittivity of 5 or higher and a coefficient ofviscosity of 0.6 cP or lower, and has a group constituting aheteroelement-containing framework (excluding carbonyl framework) and byfurther containing a monofluorophosphate and/or a difluorophosphate.

<1-1. Electrolyte>

The electrolyte to be used in nonaqueous electrolyte 2 of the inventionis not limited, and known ones for use as electrolytes in a targetnonaqueous-electrolyte secondary battery can be employed andincorporated at will. In the case where nonaqueous electrolyte 2 of theinvention is to be used in nonaqueous-electrolyte secondary batteries,the electrolyte preferably is one or more lithium salts.

Examples of the electrolyte include the same electrolytes as those shownabove with regard to nonaqueous electrolyte 1.

Preferred of these is LiPF₆, LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂,LiN(C₂F₅SO₂)₂, or lithium bis(oxalato)borate. Especially preferred isLiPF₆ or LiBF₄.

In the case of using a combination of electrolytes, the kinds of theelectrolytes and the proportions of the electrolytes are the same asthose described above with regard to nonaqueous electrolyte 1.

Furthermore, the lithium salt concentration, preferred concentration,and the like in the final composition of nonaqueous electrolyte 2 of theinvention are the same as those described above with regard tononaqueous electrolyte 1. The phenomena which occur when theconcentration is outside the range also are the same as those describedabove with regard to nonaqueous electrolyte 1.

Especially in the case where the nonaqueous solvent of the nonaqueouselectrolyte consists mainly of one or more carbonate compounds such asalkylene carbonates or dialkyl carbonates, preferred electrolytes andthe proportion thereof are the same as those described above with regardto nonaqueous electrolyte 1. The phenomena which occur when theproportion is outside the range also are the same as those describedabove with regard to nonaqueous electrolyte 1.

In the case where the nonaqueous solvent of this nonaqueous electrolyteincludes at least 50% by volume cyclic carboxylic acid ester compoundsuch as, e.g., γ-butyrolactone or γ-valerolactone, it is preferred thatLiBF₄ should account for 50 mol % or more of all lithium salts.

<1-2. Nonaqueous Solvent>

Nonaqueous electrolyte 2 of the invention contains “a compound which isliquid at 25° C., has a permittivity of 5 or higher and a coefficient ofviscosity of 0.6 cP or lower, and has a group constituting aheteroelement-containing framework (excluding carbonyl group)”.

<1-2-1. Compound which is Liquid at 25° C., has Permittivity of 5 orHigher and Coefficient of Viscosity of 0.6 cP or Lower, and has GroupConstituting Heteroelement-Containing Framework (Excluding CarbonylGroup)>

The “compound which is liquid at 25° C., has a permittivity of 5 orhigher and a coefficient of viscosity of 0.6 cP or lower, and has agroup constituting a heteroelement-containing framework (excludingcarbonyl group)” in invention 2 is not particularly limited so long asit is a compound within the scope of this definition. However, it ispreferred that the compound should be a compound having an etherframework and/or a nitrile framework in view of the properties of thenonaqueous electrolyte. Namely, a compound having at least one ethergroup or nitrile group as part of the structure is preferred.

It is more preferred that the compound having an ether framework and/ora nitrile framework should further have an alkyl group which may haveone or more substituents, from the standpoint of reducing theelectrochemical reactivity of the compound. The “alkyl group” representsan acyclic alkyl group or a cyclic alkyl group.

In the case where the compound is a compound having an ether framework,the ether framework in cooperation with an alkylene group may haveformed a saturated cyclic compound which may have one or moresubstituents. Namely, that compound may be a cyclic ether which may haveone or more substituents.

Preferred substituents of the “compound having an ether framework and/ora nitrile framework” are halogen substituents and/or “saturatedaliphatic hydrocarbon substituents having no substituents other thanhalogen atoms”, from the standpoint of the reactivity thereof.

Although such substituents of the compound preferably are halogensubstituents, alkoxycarbonyl substituents, alkoxycarboxyl substituents,and alkylcarboxyl substituents from the standpoint of the reactivitythereof, there is a fear about an increase in viscosity coefficient.Because of this, fluorine atoms are preferred as the substituents.

Examples of the “compound which is liquid at 25° C., has a permittivityof 5 or higher and a coefficient of viscosity of 0.6 cP or lower, andhas a group constituting a heteroelement-containing framework (excludingcarbonyl group)” in invention 2 include

dimethoxyethane, diethoxyethane, ethoxymethoxyethane, tetrahydrofuran,tetrahydropyran, 1,3-dioxolane, acetonitrile, propinonitrile, andfluoroacetonitrile and the like.

The permittivity of the “compound which is liquid at 25° C., has apermittivity of 5 or higher and a coefficient of viscosity of 0.6 cP orlower, and has a group constituting a heteroelement-containing framework(excluding carbonyl group)” in invention 2 is measured by the methoddescribed in The Electrochemical Society of Japan ed., Denki KagakuSokutei Manyuaru Jissen-hen, page 13. The value determined by thismeasurement is defined as permittivity in invention 2.

The coefficient of viscosity of the “compound which is liquid at 25° C.,has a permittivity of 5 or higher and a coefficient of viscosity of 0.6cP or lower, and has a group constituting a heteroelement-containingframework (excluding carbonyl group)” is measured with an Ostwaldviscometer. The value determined by this measurement is defined as thecoefficient of viscosity in invention 2. Incidentally, “cP” means“centipoises”.

It is essential that the compound should have a permittivity of 5 orhigher. The permittivity thereof is preferably 5.1 or higher, morepreferably 5.2 or higher, especially preferably 5.3 or higher. It isessential that the compound should have a coefficient of viscosity of0.6 cP or lower. The coefficient of viscosity thereof is preferably 0.5cP or lower.

When a compound having a permittivity of 5 or higher and a coefficientof viscosity of 0.6 cP or lower is used, (there is an advantage that) itis possible to produce an electrolyte which has low resistance, attainshigh ion movability, and has high infiltrating properties. In general,such compounds having a permittivity of 5 or higher and a coefficient ofviscosity of 0.6 cP or lower are susceptible to electrochemicaldecomposition. However, the electrochemical decomposition can beinhibited by using such compound in combination with amonofluorophosphate and/or a difluorophosphate.

<1-2-2. Other Nonaqueous Solvents>

Nonaqueous electrolyte 2 of the invention may contain a nonaqueoussolvent other than the “compound which is liquid at 25° C., has apermittivity of 5 or higher and a coefficient of viscosity of 0.6 cP orlower, and has a group constituting a heteroelement-containing framework(excluding carbonyl group)”, or may contain no nonaqueous solvent otherthan that compound. Nonaqueous solvents which do not adversely influencebattery characteristics after battery fabrication may be incorporatedwithout particular limitations on the use and kind thereof. Suchoptional solvents preferably are one or more members selected from thenonaqueous solvents enumerated below.

Examples of the usable nonaqueous solvents include

acyclic or cyclic carbonates, acyclic or cyclic carboxylic acid esters,phosphorus-containing organic solvents, and sulfur-containing organicsolvents and the like.

The acyclic carbonates also are not limited in the kind thereof.However, dialkyl carbonates are preferred. The number of carbon atoms ofeach constituent alkyl group is preferably 1-5, especially preferably1-4. Examples thereof include

dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate,methyl-n-propyl carbonate, ethyl n-propyl carbonate, anddi-n-propyl-carbonate and the like.

Of these, dimethyl carbonate, ethyl methyl carbonate, or diethylcarbonate is preferred from the standpoint of industrial availabilityand the reason that these compounds are satisfactory in variousproperties in a nonaqueous-electrolyte secondary battery.

The cyclic carbonates are not limited in the kind thereof. However, thenumber of carbon atoms of the alkylene group constituting each cycliccarbonate is preferably 2-6, especially preferably 2-4. Examples of thecyclic carbonate include ethylene carbonate, propylene carbonate, andbutylene carbonate (2-ethylethylene carbonate or cis- andtrans-2,3-dimethylethylene carbonates) and the like.

Of these, ethylene carbonate or propylene carbonate is preferred becausethese compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The acyclic carboxylic acid esters also are not limited in the kindthereof. Examples thereof include methyl acetate, ethyl acetate,n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate,tert-butyl acetate, methyl propionate, ethyl propionate, n-propylpropionate, isopropyl propionate, n-butyl propionate, isobutylpropionate, and tert-butyl propionate and the like.

Of these, ethyl acetate, methyl propionate, or ethyl propionate ispreferred from the standpoint of industrial availability and the reasonthat these compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The cyclic carboxylic acid esters also are not limited in the kindthereof. Examples of such esters in ordinary use includeγ-butyrolactone, γ-valerolactone, and δ-valerolactone.

Of these, γ-butyrolactone is preferred from the standpoint of industrialavailability and the reason that this compound is satisfactory invarious properties in a nonaqueous-electrolyte secondary battery.

The phosphorus-containing organic solvents also are not particularlylimited in the kind thereof. Examples thereof include

phosphoric acid esters such as trimethyl phosphate, triethyl phosphate,and triphenyl phosphate;

phosphorous acid esters such as trimethyl phosphite, triethyl phosphite,and triphenyl phosphite; and

phosphine oxides such as trimethylphosphine oxide, triethylphosphineoxide, and triphenylphosphine oxide and the like.

Furthermore, the sulfur-containing organic solvents also are notparticularly limited in the kind thereof. Examples thereof include

ethylene sulfite, 1,3-propanesultone, 1,4-butanesultone, methylmethanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone,diphenyl sulfone, methyl phenyl sulfone, dibutyl disulfide, dicyclohexyldisulfide, tetramethylthiuram monosulfide,N,N-dimethylmethanesulfonamide, and N,N-diethylmethanesulfonamide andthe like.

Of those compounds, the acyclic or cyclic carbonates or the acyclic orcyclic carboxylic acid esters are preferred because these compounds aresatisfactory in various properties in a nonaqueous-electrolyte secondarybattery. More preferred of these is ethylene carbonate, propylenecarbonate, dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, ethyl acetate, methyl propionate, ethyl propionate, orγ-butyrolactone. Even more preferred is ethylene carbonate, propylenecarbonate, dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, ethyl acetate, methyl propionate, or γ-butyrolactone.

<1-2-3. Others>

The “compound which is liquid at 25° C., has a permittivity of 5 orhigher and a coefficient of viscosity of 0.6 cP or lower, and has agroup constituting a heteroelement-containing framework (excludingcarbonyl group)” may be used alone or in combination with one or more ofthe other nonaqueous solvents shown above. However, it is preferred toemploy a combination of two or more compounds including the “compoundwhich is liquid at 25° C., has a permittivity of 5 or higher and acoefficient of viscosity of 0.6 cP or lower, and has a groupconstituting a heteroelement-containing framework (excluding carbonylgroup)”. For example, it is preferred to use a high-permittivitysolvent, such as a cyclic carbonate, in combination with a low-viscositysolvent, such as an acyclic carbonate or an acyclic ester.

For example, it is preferred to use: a combination of ahigh-permittivity solvent, e.g., a cyclic carbonate, and the “compoundwhich is liquid at 25° C., has a permittivity of 5 or higher and acoefficient of viscosity of 0.6 cP or lower, and has a groupconstituting a heteroelement-containing framework (excluding carbonylgroup)”; or a combination of a high-permittivity solvent, e.g., a cycliccarbonate, a low-viscosity solvent, e.g., an acyclic carbonate or anacyclic ester, and the “compound which is liquid at 25° C., has apermittivity of 5 or higher and a coefficient of viscosity of 0.6 cP orlower, and has a group constituting a heteroelement-containing framework(excluding carbonyl group)”. It is especially preferred to use the“compound which is liquid at 25° C., has a permittivity of 5 or higherand a coefficient of viscosity of 0.6 cP or lower, and has a groupconstituting a heteroelement-containing framework (excluding carbonylgroup)” in combination with one or more members selected from nonaqueoussolvents including cyclic carbonates and acyclic carbonates.

In particular, the total proportion of the cyclic carbonate and theacyclic carbonate to the whole nonaqueous solvent is generally 80% byvolume or higher, preferably 85% by volume or higher, more preferably90% by volume or higher. The proportion by volume of the cycliccarbonate to the sum of the cyclic carbonate and the acyclic carbonateis preferably 5% by volume or higher, more preferably 10% by volume orhigher, especially preferably 15% by volume or higher, and is generally50% by volume or lower, preferably 35% by volume or lower, morepreferably 30% by volume or lower. Use of such combination of nonaqueoussolvents is preferred because the battery fabricated with thiscombination has an improved balance between cycle characteristics andhigh-temperature storability (in particular, residual capacity andhigh-load discharge capacity after high-temperature storage).

Examples of the preferred combination including at least one cycliccarbonate and at least acyclic carbonate include: ethylene carbonate anddimethyl carbonate; ethylene carbonate and diethyl carbonate; ethylenecarbonate and ethyl methyl carbonate; ethylene carbonate, dimethylcarbonate, and diethyl carbonate; ethylene carbonate, dimethylcarbonate, and ethyl methyl carbonate; ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate; and ethylene carbonate, dimethylcarbonate, diethyl carbonate, and ethyl methyl carbonate and the like.

Combinations obtained by further adding propylene carbonate to thosecombinations including ethylene carbonate and one or more acycliccarbonates are also included in preferred combinations. In the casewhere propylene carbonate is contained, the volume ratio of the ethylenecarbonate to the propylene carbonate is preferably from 99:1 to 40:60,especially preferably from 95:5 to 50:50. It is also preferred toregulate the proportion of the propylene carbonate to the wholenonaqueous solvent to a value which is 0.1% by volume or higher,preferably 1% by volume or higher, more preferably 2% by volume orhigher, and is generally 10% by volume or lower, preferably 8% by volumeor lower, more preferably 5% by volume or lower. This is because thisregulation brings about excellent discharge load characteristics whilemaintaining the properties of the combination of ethylene carbonate andone or more acyclic carbonates.

More preferred of these are combinations including an asymmetric acycliccarbonate. In particular, combinations including ethylene carbonate, asymmetric acyclic carbonate, and an asymmetric acyclic carbonate, suchas a combination of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate, a combination of ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate, and a combination of ethylenecarbonate, dimethyl carbonate, diethyl carbonate, and ethyl methylcarbonate, or such combinations which further contain propylenecarbonate are preferred because these combinations have a satisfactorybalance between cycle characteristics and discharge loadcharacteristics. Preferred of such combinations are ones in which theasymmetric acyclic carbonate is ethyl methyl carbonate. Furthermore, thenumber of carbon atoms of each of the alkyl groups constituting eachdialkyl carbonate is preferably 1-2.

Other examples of preferred mixed solvents are ones containing anacyclic ester. In particular, the cyclic carbonate/acyclic carbonatemixed solvents which contain an acyclic ester are preferred from thestandpoint of improving the discharge load characteristics of a battery.The acyclic ester especially preferably is ethyl acetate or methylpropionate. The proportion by volume of the acyclic ester to thenonaqueous solvent is generally 5% or higher, preferably 80 or higher,more preferably 15% or higher, and is generally 50% or lower, preferably35% or lower, more preferably 30% or lower, even more preferably 25% orlower.

Other preferred examples of nonaqueous solvents are ones in which oneorganic solvent selected from the group consisting of ethylenecarbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, andγ-valerolactone or a mixed solvent composed of two or more organicsolvents selected from the group accounts for at least 60% by volume ofthe whole. Such mixed solvents have a flash point of preferably 50° C.or higher, especially preferably 70° C. or higher. The nonaqueouselectrolyte employing this solvent is reduced in solvent vaporizationand liquid leakage even when used at high temperatures. In particular,when such a nonaqueous solvent which includes ethylene carbonate andγ-butyrolactone in a total amount of 80% by volume or larger, preferably90% by volume or larger, based on the nonaqueous solvent and in whichthe volume ratio of the ethylene carbonate to the γ-butyrolactone isfrom 5:95 to 45:55 or such a nonaqueous solvent which includes ethylenecarbonate and propylene carbonate in a total amount of 80% by volume orlarger, preferably 90% by volume or larger, based on the wholenonaqueous solvent and in which the volume ratio of the ethylenecarbonate to the propylene carbonate is from 30:70 to 80:20 is used,then an improved balance between cycle characteristics and dischargeload characteristics, etc. is generally obtained.

<1-3. Monofluorophosphate and Difluorophosphate>

Nonaqueous electrolyte 2 of the invention contains a monofluorophosphateand/or a difluorophosphate as an essential component. With respect tothe “monofluorophosphate and difluorophosphate” to be used in invention2, the kinds and contents thereof, places where the salts exist, methodsof analysis, production process, etc. are the same as those describedabove with regard to nonaqueous electrolyte 1.

<1-4. Additives>

Nonaqueous electrolyte 2 of the invention may contain various additivesso long as these additives do not considerably lessen the effects ofinvention 2. In the case where additives are additionally incorporatedto prepare the nonaqueous electrolyte, conventionally known additivescan be used at will. One additive may be used alone, or any desiredcombination of two or more additives in any desired proportion may beused.

Examples of the additives include overcharge inhibitors and aids forimproving capacity retentivity after high-temperature storage and cyclecharacteristics. It is preferred to add a carbonate having at leasteither of an unsaturated bond and a halogen atom (hereinafter sometimesreferred to as “specific carbonate”) as an aid for improving capacityretentivity after high-temperature storage and cycle characteristics,among those additives. The specific carbonate and other additives areseparately explained below.

<1-4-1. Specific Carbonate>

The specific carbonate is a carbonate having at least either of anunsaturated bond and a halogen atom. The specific carbonate may have anunsaturated bond only or have a halogen atom only, or may have both anunsaturated bond and a halogen atom.

The molecular weight of the specific carbonate is not particularlylimited, and may be any desired value unless this considerably lessensthe effects of invention 2. However, the molecular weight thereof isgenerally 50 or higher, preferably 80 or higher, and is generally 250 orlower, preferably 150 or lower. When the molecular weight thereof is toohigh, this specific carbonate has reduced solubility in the nonaqueouselectrolyte and there are cases where the effect of the carbonate isdifficult to produce sufficiently.

Processes for producing the specific carbonate also are not particularlylimited, and a known process selected at will can be used to produce thecarbonate.

Any one specific carbonate may be incorporated alone into nonaqueouselectrolyte 2 of the invention, or any desired combination of two ormore specific carbonates may be incorporated thereinto in any desiredproportion.

The amount of the specific carbonate to be incorporated into nonaqueouselectrolyte 2 of the invention is not limited, and may be any desiredvalue unless this considerably lessens the effects of invention 2. Itis, however, desirable that the specific carbonate should beincorporated in a concentration which is generally 0.01% by mass orhigher, preferably 0.1% by mass or higher, more preferably 0.3% by massor higher, and is generally 70% by mass or lower, preferably 50% by massor lower, more preferably 40% by mass or lower, based on nonaqueouselectrolyte 2 of the invention.

When the amount of the specific carbonate is below the lower limit ofthat range, there are cases where use of this nonaqueous electrolyte 2of the invention in a nonaqueous-electrolyte secondary battery resultsin difficulties in producing the effect of sufficiently improving thecycle characteristics of the nonaqueous-electrolyte secondary battery.On the other hand, when the proportion of the specific carbonate is toohigh, there is a tendency that use of this nonaqueous electrolyte 2 ofthe invention in a nonaqueous-electrolyte secondary battery results indecreases in the high-temperature storability and continuous-chargecharacteristics of the nonaqueous-electrolyte secondary battery. Inparticular, there are cases where gas evolution is enhanced and capacityretentivity decreases.

<1-4-1-1. Unsaturated Carbonate>

The carbonate having an unsaturated bond (hereinafter often referred toas “unsaturated carbonate”) is the same as in nonaqueous electrolyte 1.

<1-4-1-2. Halogenated Carbonate>

On the other hand, the carbonate having a halogen atom (hereinafteroften referred to as “halogenated carbonate”) as one form of thespecific carbonate according to invention 2 is not particularly limitedso long as it is a carbonate having a halogen atom, and any desiredhalogenated carbonate can be used. The same carbonates as those shownabove under “Carbonate Having Halogen Atom” with regard to nonaqueouselectrolyte 1 can be used. Of these examples, preferred embodiments ofthe “halogenated carbonate” in nonaqueous electrolyte 2 are shown below.

Examples of the halogen atoms include fluorine, chlorine, bromine, andiodine atoms. Preferred of these are fluorine atoms or chlorine atoms.Especially preferred are fluorine atoms. The number of halogen atomspossessed by the halogenated carbonate also is not particularly limitedso long as the number thereof is 1 or larger. However, the numberthereof is generally 6 or smaller, preferably 4 or smaller. In the casewhere the halogenated carbonate has two or more halogen atoms, theseatoms may be the same or different.

Examples of the halogenated carbonate include ethylene carbonatederivatives, dimethyl carbonate derivatives, ethyl methyl carbonatederivatives, and diethyl carbonate derivatives.

Examples of the ethylene carbonate derivatives include

fluoroethylene carbonate, chloroethylene carbonate, 4,4-difluoroethylenecarbonate, 4,5-difluoroethylene carbonate, 4,4-dichloroethylenecarbonate, 4,5-dichloroethylene carbonate, 4-fluoro-4-methylethylenecarbonate, 4-chloro-4-methylethylene carbonate,4,5-difluoro-4-methylethylene carbonate, 4,5-dichloro-4-methylethylenecarbonate, 4-fluoro-5-methylethylene carbonate,4-chloro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylenecarbonate, 4,4-dichloro-5-methylethylene carbonate,4-(fluoromethyl)-ethylene carbonate, 4-(chloromethyl)-ethylenecarbonate, 4-(difluoromethyl)-ethylene carbonate,4-(dichloromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylenecarbonate, 4-(trichloromethyl)-ethylene carbonate,4-(fluoromethyl)-4-fluoroethylene carbonate,4-(chloromethyl)-4-chloroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-(chloromethyl)-5-chloroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate, 4-chloro-4,5-dimethylethylenecarbonate, 4,5-difluoro-4,5-dimethylethylene carbonate,4,5-dichloro-4,5-dimethylethylene carbonate,4,4-difluoro-5,5-dimethylethylene carbonate, and4,4-dichloro-5,5-dimethylethylene carbonate and the like.

Examples of the dimethyl carbonate derivatives include

fluoromethyl methyl carbonate, difluoromethyl methyl carbonate,trifluoromethyl methyl carbonate, bis(fluoromethyl)carbonate,bis(difluoro)methyl carbonate, bis(trifluoro)methyl carbonate,chloromethyl methyl carbonate, dichloromethyl methyl carbonate,trichloromethyl methyl carbonate, bis(chloromethyl)carbonate,bis(dichloro)methyl carbonate, and bis(trichloro)methyl carbonate andthe like.

Examples of the ethyl methyl carbonate derivatives include

2-fluoroethyl methyl carbonate, ethyl fluoromethyl carbonate,2,2-difluoroethyl methyl carbonate, 2-fluoroethyl fluoromethylcarbonate, ethyl difluoromethyl carbonate, 2,2,2-trifluoroethyl methylcarbonate, 2,2-difluoroethyl fluoromethyl carbonate, 2-fluoroethyldifluoromethyl carbonate, ethyl trifluoromethyl carbonate, 2-chloroethylmethyl carbonate, ethyl chloromethyl carbonate, 2,2-dichloroethyl methylcarbonate, 2-chloroethyl chloromethyl carbonate, ethyl dichloromethylcarbonate, 2,2,2-trichloroethyl methyl carbonate, 2,2-dichloroethylchloromethyl carbonate, 2-chloroethyl dichloromethyl carbonate, andethyl trichloromethyl carbonate and the like.

Examples of the diethyl carbonate derivatives includeEthyl-(2-fluoroethyl)carbonate, ethyl-(2,2-difluoroethyl)carbonate,bis(2-fluoroethyl)carbonate, ethyl-(2,2,2-trifluoroethyl)carbonate,2,2-difluoroethyl-2′-fluoroethyl carbonate,bis(2,2-difluoroethyl)carbonate, 2,2,2-trifluoroethyl-2′-fluoroethylcarbonate, 2,2,2-trifluoroethyl-2′,2′-difluoroethyl carbonate,bis(2,2,2-trifluoroethyl)carbonate, ethyl-(2-chloroethyl)carbonate,ethyl-(2,2-dichloroethyl)carbonate, bis(2-chloroethyl)carbonate,ethyl-(2,2,2-trichloroethyl)carbonate, 2,2-dichloroethyl-2′-chloroethylcarbonate, bis(2,2-dichloroethyl)carbonate,2,2,2-trichloroethyl-2′-chloroethyl carbonate,2,2,2-trichloroethyl-2′,2′-dichloroethyl carbonate, andbis(2,2,2-trichloroethyl)carbonate and the like.

Preferred of these halogenated carbonates are the carbonates having afluorine atom. More preferred are the ethylene carbonate derivativeshaving a fluorine atom. In particular, fluoroethylene carbonate,4-(fluoromethyl)-ethylene carbonate, 4,4-difluoroethylene carbonate, and4,5-difluoroethylene carbonate are more suitable because thesecarbonates form an interface-protective coating film.

<1-4-1-3. Halogenated Unsaturated Carbonate>

Furthermore usable as the specific carbonate is a carbonate having bothan unsaturated bond and a halogen atom (this carbonate is suitablyreferred to as “halogenated unsaturated carbonate”). This halogenatedunsaturated carbonate is not particularly limited, and any desiredhalogenated unsaturated carbonate can be used unless the effects ofinvention 2 are considerably lessened thereby.

Examples of the halogenated unsaturated carbonate include vinylenecarbonate derivatives, ethylene carbonate derivatives substituted withone or more aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond, and allyl carbonates.

Examples of the vinylene carbonate derivatives include

fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate,4-fluoro-5-phenylvinylene carbonate, 4-(trifluoromethyl)vinylenecarbonate, chlorovinylene carbonate, 4-chloro-5-methylvinylenecarbonate, 4-chloro-5-phenylvinylene carbonate, and4-(trichloromethyl)vinylene carbonate and the like.

Examples of the ethylene carbonate derivatives substituted with one ormore aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond include

4-fluoro-4-vinylethylene carbonate, 4-fluoro-5-vinylethylene carbonate,4,4-difluoro-5-vinylethylene carbonate, 4,5-difluoro-4-vinylethylenecarbonate, 4-chloro-5-vinylethylene carbonate,4,4-dichloro-5-vinylethylene carbonate, 4,5-dichloro-4-vinylethylenecarbonate, 4-fluoro-4,5-divinylethylene carbonate,4,5-difluoro-4,5-divinylethylene carbonate, 4-chloro-4,5-divinylethylenecarbonate, 4,5-dichloro-4,5-divinylethylene carbonate,4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylenecarbonate, 4,4-difluoro-5-phenylethylene carbonate,4,5-difluoro-4-phenylethylene carbonate, 4-chloro-4-phenylethylenecarbonate, 4-chloro-5-phenylethylene carbonate,4,4-dichloro-5-phenylethylene carbonate, 4,5-dichloro-4-phenylethylenecarbonate, 4,5-difluoro-4,5-diphenylethylene carbonate, and4,5-dichloro-4,5-diphenylethylene carbonate and the like.

Examples of phenyl carbonates include

fluoromethyl phenyl carbonate, 2-fluoroethyl phenyl carbonate,2,2-difluoroethyl phenyl carbonate, 2,2,2-trifluoroethyl phenylcarbonate, chloromethyl phenyl carbonate, 2-chloroethyl phenylcarbonate, 2,2-dichloroethyl phenyl carbonate, and 2,2,2-trichloroethylphenyl carbonate and the like.

Examples of vinyl carbonates include

fluoromethyl vinyl carbonate, 2-fluoroethyl vinyl carbonate,2,2-difluoroethyl vinyl carbonate, 2,2,2-trifluoroethyl vinyl carbonate,chloromethyl vinyl carbonate, 2-chloroethyl vinyl carbonate,2,2-dichloroethyl vinyl carbonate, and 2,2,2-trichloroethyl vinylcarbonate and the like.

Examples of the allyl carbonates include

fluoromethyl allyl carbonate, 2-fluoroethyl allyl carbonate,2,2-difluoroethyl allyl carbonate, 2,2,2-trifluoroethyl allyl carbonate,chloromethyl allyl carbonate, 2-chloroethyl allyl carbonate,2,2-dichloroethyl allyl carbonate, and 2,2,2-trichloroethyl allylcarbonate and the like.

It is especially preferred to use, as the specific carbonate, one ormore members selected from the group consisting of vinylene carbonate,vinylethylene carbonate, fluoroethylene carbonate, 4,5-difluoroethylenecarbonate, and derivatives of these, among the examples of thehalogenated unsaturated carbonate enumerated above. These carbonates arehighly effective even when used alone.

<1-4-2. Other Additives>

Examples of additives other than the specific carbonate includeovercharge inhibitors and aids for improving capacity retentivity afterhigh-temperature storage and cycle characteristics. The “overchargeinhibitors” and the “aids for improving capacity retentivity afterhigh-temperature storage and cycle characteristics” are the same asthose described above with regard to nonaqueous electrolyte 1.

[2. Nonaqueous-Electrolyte Secondary Battery]

Nonaqueous-electrolyte secondary battery 2 of the invention includes: anegative electrode and a positive electrode which are capable ofoccluding and releasing ions; and the nonaqueous electrolyte of thisinvention.

<2-1. Battery Constitution>

Nonaqueous-electrolyte secondary battery 2 of the invention may have thesame battery constitution as that described above with regard tononaqueous-electrolyte secondary battery 1.

<2-2. Nonaqueous Electrolyte>

As the nonaqueous electrolyte, the nonaqueous electrolyte 2 of theinvention described above is used. Incidentally, a mixture of nonaqueouselectrolyte 2 of the invention and another nonaqueous electrolyte may beused so long as this is not counter to the spirit of invention 2.

<2-3. Negative Electrode>

The negative electrode of nonaqueous-electrolyte secondary battery 2 maybe the same as the negative electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-4. Positive Electrode>

The positive electrode of nonaqueous-electrolyte secondary battery 2 maybe the same as the positive electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-5. Separator>

The separator of nonaqueous-electrolyte secondary battery 2 may be thesame as the separator described above with regard tononaqueous-electrolyte secondary battery 1.

<2-6. Battery Design>

The battery design of nonaqueous-electrolyte secondary battery 2 may bethe same as the battery design described above with regard tononaqueous-electrolyte secondary battery 1.

<Nonaqueous Electrolyte 3 and Nonaqueous-Electrolyte Secondary Battery3>

[1. Nonaqueous Electrolyte]

Nonaqueous electrolyte 3 of the invention is a nonaqueous electrolytemainly comprising a nonaqueous solvent and an electrolyte dissolvedtherein, the nonaqueous electrolyte containing a monofluorophosphateand/or a difluorophosphate and further containing “at least one compoundselected from the group consisting of compounds represented by generalformula (1) given above, nitrile compounds, isocyanate compounds,phosphazene compounds, disulfonic acid ester compounds, sulfidecompounds, disulfide compounds, acid anhydrides, lactone compoundshaving a substituent in the α-position, and compounds having acarbon-carbon triple bond”. Hereinafter, the at least one compound givenin the quotation marks is referred to as “compound A of invention 3”.

<1-1. Electrolyte>

Nonaqueous electrolyte 3 of the invention includes an electrolyte and anonaqueous solvent containing the electrolyte dissolved therein. Theelectrolyte to be used in nonaqueous electrolyte 3 of the invention isnot limited, and known ones for use as electrolytes in a targetnonaqueous-electrolyte secondary battery can be employed andincorporated at will. In the case where nonaqueous electrolyte 3 of theinvention is to be used in nonaqueous-electrolyte secondary batteries,one or more lithium salts are preferable of the electrolyte.

The electrolyte for use in nonaqueous electrolyte 3 of the invention isthe same as that described above with regard to nonaqueous electrolyte 1of the invention.

<1-2. Compound A of Invention 3>

Nonaqueous electrolyte 3 of the invention contains the “compound A ofinvention 3”. “Compound A of invention 3” may be a compound representedby general formula (5), nitrile compound, isocyanate compound,phosphazene compound, disulfonic acid ester compound, sulfide compounds,disulfide compound, acid anhydride, lactone compound having asubstituent in the α-position, or compound having a carbon-carbon triplebond. The compounds constituting the group of compounds for “compound Aof invention 3” in invention 3 are explained below in more detail.

<1-2-1. Compounds Represented by General Formula (5)>

[In general formula (5), R¹, R², and R³ each independently represent afluorine atom, an alkyl group which has 1-12 carbon atoms and may besubstituted with a fluorine atom, or an alkoxy group which has 1-12carbon atoms and may be substituted with a fluorine atom.]

The alkyl group having 1-12 carbon atoms is not particularly limited.Examples thereof include acyclic or cyclic alkyl groups havingpreferably 1-8, more preferably 1-6 carbon atoms. Preferred of these arethe acyclic alkyl groups. Specific examples thereof include methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl,pentyl, cyclopentyl, and cyclohexyl and the like.

The alkoxy group having 1-12 carbon atoms is not particularly limited.However, this group preferably is an alkoxy group having 1-8 carbonatoms, especially preferably 1-6 carbon atoms. Examples thereof includemethoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy,and tert-butoxy and the like.

Examples of the alkyl group substituted with a fluorine atom includetrifluoromethyl, trifluoroethyl, and pentafluoroethyl and the like.

Examples of the alkoxy group substituted with a fluorine atom includetrifluoromethoxy, trifluoroethoxy, and pentafluoroethoxy.

Examples of the compound in which all of R¹, R², and R³ are alkoxygroups include

trimethyl phosphate, ethyl dimethyl phosphate, dimethyl n-propylphosphate, n-butyl dimethyl phosphate, diethyl methyl phosphate, ethyln-propyl methyl phosphate, n-butyl ethyl methyl phosphate, di-n-propylmethyl phosphate, n-butyl n-propyl methyl phosphate, di-n-butyl methylphosphate, triethyl phosphate, diethyl n-propyl phosphate, n-butyldiethyl phosphate, di-n-propyl ethyl phosphate, n-butyl n-propyl ethylphosphate, di-n-butyl ethyl phosphate, tri-n-propyl phosphate, n-butyldi-n-propyl phosphate, di-n-butyl n-propyl phosphate, tri-n-butylphosphate, cyclopentyl dimethyl phosphate, cyclopentyl diethylphosphate, cyclopentyl di-n-propyl phosphate, cyclopentyl di-n-butylphosphate, cyclopentyl ethyl methyl phosphate, dicyclopentyl methylphosphate, tricyclopentyl phosphate, cyclohexyl dimethyl phosphate,cyclohexyl diethyl phosphate, cyclohexyl di-n-propyl phosphate,cyclohexyl di-n-butyl phosphate, cyclohexyl ethyl methyl phosphate,dicyclohexyl methyl phosphate, tricyclohexyl phosphate, dimethyltrifluoromethyl phosphate, diethyl trifluoromethyl phosphate, ethylmethyl trifluoromethyl phosphate, (2,2,2-trifluoroethyl)dimethylphosphate, diethyl(2,2,2-trifluoroethyl)phosphate,ethyl(2,2,2-trifluoroethyl)methyl phosphate, (pentafluoroethyl)dimethylphosphate, diethyl(pentafluoroethyl)phosphate,ethyl(pentafluoroethyl)methyl phosphate, bis(trifluoromethyl)methylphosphate, tris(trifluoromethyl)phosphate,bis(2,2,2-trifluoroethyl)methyl phosphate,bis(2,2,2-trifluoroethyl)trifluoromethyl phosphate,bis(pentafluoroethyl)methyl phosphate,bis(pentafluoroethyl)trifluoromethyl phosphate,bis(trifluoromethyl)ethyl phosphate, bis(trifluoromethyl)2,2,2-trifluoroethyl phosphate, bis(trifluoromethyl)pentafluoroethylphosphate, bis(2,2,2-trifluoroethyl)ethyl phosphate,tris(2,2,2-trifluoroethyl)phosphate,bis(2,2,2,-trifloroethyl)pentafluoroethyl phosphate,bis(pentafluoroethyl)ethyl phosphate,bis(pentafluoroethyl)-2,2,2-trifluoroethyl phosphate, andtris(pentafluoroethyl)phosphate and the like.

Preferred of the phosphoric acid esters enumerated above are

trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate,triethyl phosphate, dimethyl trifluoromethyl phosphate, diethyltrifluoromethyl phosphate, ethyl methyl trifluoromethyl phosphate,(2,2,2-trifluoroethyl)dimethyl phosphate,diethyl(2,2,2-trifluoroethyl)phosphate,ethyl(2,2,2-trifluoroethyl)methyl phosphate, (pentafluoroethyl)dimethylphosphate, diethyl(pentafluoroethyl)phosphate,ethyl(pentafluoroethyl)methyl phosphate,bis(trifluoromethyl)methyl phosphate, tris(trifluoromethyl)phosphate,bis(2,2,2-trifluoroethyl)methyl phosphate,bis(2,2,2-trifluoroethyl)trifluoromethyl phosphate,bis(pentafluoroethyl)methyl phosphate,bis(pentafluoroethyl)trifluoromethyl phosphate,bis(trifluoromethyl)ethyl phosphate,bis(trifluoromethyl)-2,2,2-trifluoroethyl phosphate,bis(trifluoromethyl)pentafluoroethyl phosphate,bis(2,2,2-trifluoroethyl)ethyl phosphate,tris(2,2,2-trifluoroethyl)phosphate,bis(2,2,2,-trifloroethyl)pentafluoroethyl phosphate,bis(pentafluoroethyl)ethyl phosphate,bis(pentafluoroethyl)-2,2,2-trifluoroethyl phosphate,tris(pentafluoroethyl)phosphate, and the like.

Examples of the compound in which any one of R¹, R², and R³ is an alkylgroup and any two of these are alkoxy groups include

dimethyl methylphosphonate, diethyl ethylphosphonate, di-n-propyln-propylphosphonate, diisopropyl isopropylphosphonate, di-n-butyln-butylphosphonate, diisobutyl isobutylphosphonate, di-tert-butyltert-butylphosphonate, dicyclopentyl cyclopentylphosphonate,dicyclohexyl cyclohexylphosphonate, diethyl methylphosphonate,di-n-propyl methylphosphonate, di-n-butyl methylphosphonate,dicyclopentyl methylphosphonate, dicyclohexyl methylphosphonate,dimethyl ethylphosphonate, di-n-propyl ethylphosphonate, di-n-butylethylphosphonate, dicyclopentyl ethylphosphonate, dicyclohexylethylphosphonate, dimethyl n-propylphosphonate, diethyln-propylphosphonate, dimethyl n-butylphosphonate, diethyln-butylphosphonate, dimethyl cyclohexylphosphonate, diethylcyclohexylphosphonate, ethyl methyl methylphosphonate, methyl n-propylmethylphosphonate, n-butyl methyl methylphosphonate, cyclopentyl methylmethylphosphonate, cyclohexyl methyl methylphosphonate, ethyl n-propylmethylphosphonate, cyclohexyl ethyl methylphosphonate, ethyl methylethylphosphonate, methyl n-propyl ethylphosphonate, n-butyl methylethylphosphonate, cyclopentyl methyl ethylphosphonate, cyclohexyl methylethylphosphonate, ethyl n-propyl ethylphosphonate, cyclohexyl ethylethylphosphonate, ethyl methyl n-propylphosphonate, methyl n-propyln-propylphosphonate, n-butyl methyl n-propylphosphonate, cyclopentylmethyl n-propylphosphonate, cyclohexyl methyl n-propylphosphonate, ethyln-propyl n-propylphosphonate, cyclohexyl ethyl n-propylphosphonate,ethyl methyl n-butylphosphonate, methyl n-propyl n-butylphosphonate,n-butyl methyl n-butylphosphonate, cyclopentyl methyln-butylphosphonate, cyclohexyl methyl n-butylphosphonate, ethyl n-propyln-butylphosphonate, cyclohexyl ethyl n-butylphosphonate,ethyl methyl cyclohexylphosphonate, methyl n-propylcyclohexylphosphonate, n-butyl methyl cyclohexylphosphonate, cyclopentylmethyl cyclohexylphosphonate, cyclohexyl methyl cyclohexylphosphonate,ethyl n-propyl cyclohexylphosphonate, cyclohexyl ethylcyclohexylphosphonate, diperfluoromethyl methylphosphonate,di(2,2,2-trifluoroethyl)methylphosphonate, diperfluoroethylmethylphosphonate, di(2-fluorocyclohexyl)methylphosphonate,di(3-fluorocyclohexyl)methylphosphonate,di(4-fluorocyclohexyl)methylphosphonate, diperfluoromethylethylphosphonate, di(2,2,2,-trifluoroethyl)ethylphosphonate,diperfluoroethyl ethylphosphonate,di(2-fluorocyclohexyl)ethylphosphonate,di(3-fluorocyclohexyl)ethylphosphonate,di(4-fluorocyclohexyl)ethylphosphonate, di(2,2,2-trifluoroethyl)n-propylphosphonate, diperfluoroethyl n-propylphosphonate,di(2,2,2-trifluoroethyl) n-butylphosphonate, diperfluoroethyln-butylphosphonate, di(2,2,2-trifluoroethyl)cyclohexylphosphonate,diperfluoroethyl cyclohexylphosphonate,methyl perfluoromethyl methylphosphonate,methyl(2,2,2-trifluoroethyl)methylphosphonate, methyl perfluoroethylmethylphosphonate, (2-fluorocyclohexyl)methyl methylphosphonate,(3-fluorocyclohexyl)methyl methylphosphonate, (4-fluorocyclohexyl)methylmethylphosphonate, ethyl perfluoroethyl methylphosphonate,cyclohexyl(2,2,2-trifluoroethyl)methylphosphonate, cyclohexylperfluoroethyl methylphosphonate,perfluoroethyl(2,2,2-trifluoroethyl)methylphosphonate,ethyl(2,2,2-trifluoroethyl)ethylphosphonate, ethyl perfluoroethylethylphosphonate, cyclohexyl(2,2,2-trifluoroethyl)ethylphosphonate,cyclohexyl perfluoroethyl ethylphosphonate,perfluoroethyl(2,2,2-trifluoroethyl)ethylphosphonate,(2-fluorocyclohexyl) (2,2,2-trifluoroethyl)ethylphosphonate,ethyl(2,2,2-trifluoroethyl) n-propylphosphonate, ethyl perfluoroethyln-propylphosphonate, cyclohexyl(2,2,2-trifluoroethyl)n-propylphosphonate, cyclohexyl perfluoroethyl n-propylphosphonate,perfluoroethyl(2,2,2-trifluoroethyl) n-propylphosphonate,(2-fluorocyclohexyl) (2,2,2-trifluoroethyl) n-propylphosphonate,ethyl(2,2,2-trifluoroethyl) n-butylphosphonate, ethyl perfluoroethyln-butylphosphonate, cyclohexyl(2,2,2-trifluoroethyl) n-butylphosphonate,cyclohexyl perfluoroethyl n-butylphosphonate,perfluoroethyl(2,2,2-trifluoroethyl) n-butylphosphonate,(2-fluorocyclohexyl) (2,2,2-trifluoroethyl) n-butylphosphonate,ethyl(2,2,2-trifluoroethyl)cyclohexylphosphonate, ethyl perfluoroethylcyclohexylphosphonate,cyclohexyl(2,2,2-trifluoroethyl)cyclohexylphosphonate, cyclohexylperfluoroethyl cyclohexylphosphonate,perfluoroethyl(2,2,2-trifluoroethyl)cyclohexylphosphonate,(2-fluorocyclohexyl) (2,2,2-trifluoroethyl)cyclohexylphosphonate,diperfluoromethyl perfluoromethylphosphonate, di(2,2,2-trifluoroethyl)(2,2,2-trifluoroethyl)phosphonate, diperfluoroethylperfluoroethylphosphonate, di(2-fluorocyclohexyl)(2-fluorocyclohexyl)phosphonate, di(3-fluorocyclohexyl)(3-fluorocyclohexyl)phosphonate, di(4-fluorocyclohexyl)(4-fluorocyclohexyl)phosphonate,dimethyl(2,2,2-trifluoroethyl)phosphonate,diethyl(2,2,2-trifluoroethyl)phosphonate,di-n-butyl(2,2,2-trifluoroethyl)phosphonate,dicyclohexyl(2,2,2-trifluoroethyl)phosphonate,diperfluoroethyl(2,2,2-trifluoroethyl)phosphonate,di(2-fluorocyclohexyl) (2,2,2-trifluoroethyl)phosphonate, ethylmethyl(2,2,2-trifluoroethyl)phosphonate, n-butylmethyl(2,2,2-trifluoroethyl)phosphonate, cyclohexylmethyl(2,2,2-trifluoroethyl)phosphonate, methyl(2,2,2-trifluoroethyl)(2,2,2-trifluoroethyl)phosphonate, methylperfluoroethyl(2,2,2-trifluoroethyl)phosphonate,(2-fluorocyclohexyl)methyl(2,2,2-trifluoroethyl)phosphonate, cyclohexylethyl(2,2,2-trifluoroethyl)phosphonate, ethyl(2,2,2-trifluoroethyl)(2,2,2-trifluoroethyl)phosphonate, cyclohexyl(2,2,2-trifluoroethyl)(2,2,2-trifluoroethyl)phosphonate,dimethyl(2-fluorocyclohexyl)phosphonate,diethyl(2-fluorocyclohexyl)phosphonate,dicyclohexyl(2-fluorocyclohexyl)phosphonate, bis(2,2,2-trifluoroethyl)(2-fluorocyclohexyl)phosphonate, ethylmethyl(2-fluorocyclohexyl)phosphonate, cyclohexylmethyl(2-fluorocyclohexyl)phosphonate, and methyl(2,2,2-trifluoroethyl)(2-fluorocyclohexyl)phosphonate.

Preferred of the phosphonic acid esters enumerated above are

dimethyl methylphosphonate, diethyl ethylphosphonate, di-n-propyln-propylphosphonate, di-n-butyl n-butylphosphonate, diisobutylisobutylphosphonate, diethyl methylphosphonate, di-n-butylmethylphosphonate, dimethyl ethylphosphonate, di-n-propylethylphosphonate, dimethyl n-propylphosphonate, diethyln-propylphosphonate, di(2,2,2-trifluoroethyl)methylphosphonate,di(2,2,2-trifluoroethyl)ethylphosphonate, diperfluoromethylperfluoromethylphosphonate, di(2,2,2-trifluoroethyl)(2,2,2-trifluoroethyl)phosphonate, diperfluoroethylperfluoroethylphosphonate, dimethyl(2,2,2-trifluoroethyl)phosphonate,and diethyl(2,2,2-trifluoroethyl)phosphonate.

Examples of the compound in which any two of R¹, R², and R³ are alkylgroups and any one of these is an alkoxy group include

methyl dimethylphosphinate, ethyl diethylphosphinate, n-propyldi-n-propylphosphinate, isopropyl diisopropylphosphinate, n-butyldi-n-butylphosphinate, isobutyl diisobutylphosphinate, tert-butyldi-tert-butylphosphinate, cyclopentyl dicyclopentylphosphinate,cyclohexyl dicyclohexylphosphinate, methyl diethylphosphinate, methyldi-n-propylphosphinate, methyl diisopropylphosphinate, methyldi-n-butylphosphinate, methyl diisobutylphosphinate, methyldi-tert-butylphosphinate, methyl dicyclopentylphosphinate, methyldicyclohexylphosphinate, ethyl dimethylphosphinate, ethyldi-n-propylphosphinate, ethyl diisopropylphosphinate, ethyldi-n-butylphosphinate, ethyl diisobutylphosphinate, ethyldi-tert-butylphosphinate, ethyl dicyclopentylphosphinate, ethyldicyclohexylphosphinate, n-propyl dimethylphosphinate, n-propyldiethylphosphinate, n-propyl diisopropylphosphinate, n-propyldi-n-butylphosphinate, n-propyl diisobutylphosphinate, n-propyldi-tert-butylphosphinate, n-propyl dicyclopentylphosphinate, n-propyldicyclohexylphosphinate, n-butyl dimethylphosphinate, n-butyldiethylphosphinate, n-butyl dicyclohexylphosphinate, cyclohexyldimethylphosphinate, cyclohexyl diethylphosphinate, cyclohexyldi-n-propylphosphinate, cyclohexyl di-n-butylphosphinate, methylethylmethylphosphinate, methyl methyl-n-propylphosphinate, methyln-butylmethylphosphinate, methyl cyclohexylmethylphosphinate, methylethyl-n-propylphosphinate, methyl n-butylethylphosphinate, methylcyclohexylethylphosphinate, methyl cyclohexyl-n-propylphosphinate,methyl n-butylcyclohexylphosphinate, ethyl ethylmethylphosphinate, ethylmethyl-n-propylphosphinate, ethyl n-butylmethylphosphinate, ethylcyclohexylmethylphosphinate, ethyl n-butylethylphosphinate, ethylcyclohexylethylphosphinate, ethyl n-butylcyclohexylphosphinate, n-butylethylmethylphosphinate, n-butyl methyl-n-butylphosphinate, n-butylcyclohexylmethylphosphinate, n-butyl methylphenylphosphinate, n-butyln-butylethylphosphinate, n-butyl cyclohexylethylphosphinate, n-butylethylphenylphosphinate, n-butyl n-butylcyclohexylphosphinate, n-butylcyclohexylvinylphosphinate, cyclohexyl ethylmethylphosphinate,cyclohexyl methyl-n-butylphosphinate, cyclohexylcyclohexylmethylphosphinate, cyclohexyl n-butylethylphosphinate,cyclohexyl cyclohexylethylphosphinate, cyclohexyln-butylcyclohexylphosphinate, perfluoromethylbisperfluoromethylphosphinate,(2,2,2-trifluoroethyl)bis(2,2,2-trifluoroethyl)phosphonate,perfluoroethyl bisperfluoroethylphosphinate,(2-fluorocyclohexyl)di(2-fluorocyclohexyl)phosphinate,(3-fluorocyclohexyl)di(3-fluorocyclohexyl)phosphinate,(4-fluorocyclohexyl)di(4-fluorocyclohexyl)phosphinate, methylbisperfluoromethylphosphinate, methylbis(2,2,2-trifluoroethyl)phosphinate, methylbisperfluoroethylphosphinate, methyl di(2-fluorocyclohexyl)phosphinate,methyl di(3-fluorocyclohexyl)phosphinate, methyldi(4-fluorocyclohexyl)phosphinate, ethyl bisperfluoromethylphosphinate,ethyl bis(2,2,2-trifluoroethyl)phosphinate, ethylbisperfluoroethylphosphinate, ethyl di(2-fluorocyclohexyl)phosphinate,ethyl di(3-fluorocyclohexyl)phosphinate, ethyldi(4-fluorocyclohexyl)phosphinate, n-butylbis(2,2,2-trifluoroethyl)phosphinate, cyclohexylbis(2,2,2-trifluoroethyl)phosphinate,(2,2,2-trifluoroethyl)dimethylphosphinate, (2,2,2-trifluoroethyl)diethylphosphinate, (2,2,2-trifluoroethyl)di-n-butylphosphinate,(2,2,2-trifluoroethyl)dicyclohexylphosphinate, ethylmethyl(2,2,2-trifluoroethyl)phosphinate, ethylmethyl(2-fluorophenyl)phosphinate, ethylethyl(2,2,2-trifluoroethyl)phosphinate, ethyln-butyl(2,2,2-trifluoroethyl)phosphinate, ethylcyclohexyl(2,2,2-trifluoroethyl)phosphinate, n-butylmethyl(2,2,2-trifluoroethyl)phosphinate, n-butylethyl(2,2,2-trifluoroethyl)phosphinate, n-butyln-butyl(2,2,2-trifluoroethyl)phosphinate, n-butylcyclohexyl(2,2,2-trifluoroethyl)phosphinate, cyclohexylmethyl(2,2,2-trifluoroethyl)phosphinate, cyclohexylethyl(2,2,2-trifluoroethyl)phosphinate, cyclohexyln-butyl(2,2,2-trifluoroethyl)phosphinate, cyclohexylcyclohexyl(2,2,2-trifluoroethyl)phosphinate,(2,2,2-trifluoroethyl)ethylmethylphosphinate,(2,2,2-trifluoroethyl)methyl-n-butylphosphinate,(2,2,2-trifluoroethyl)cyclohexylmethylphosphinate,(2,2,2-trifluoroethyl)methyl(2,2,2-trifluoroethyl)phosphinate,(2,2,2-trifluoroethyl) n-butylethylphosphinate,(2,2,2-trifluoroethyl)cyclohexylethylphosphinate,(2,2,2-trifluoroethyl)ethyl(2,2,2-trifluoroethyl)phosphinate,(2,2,2-trifluoroethyl) n-butylcyclohexylphosphinate,(2,2,2-trifluoroethyl) n-butyl(2,2,2-trifluoroethyl)phosphinate,(2,2,2-trifluoroethyl)cyclohexyl(2,2,2-trifluoroethyl)phosphinate, and(2,2,2-trifluoroethyl) (2,2,2-trifluoroethyl)phenylphosphinate, and thelike.

Preferred of the phosphinic acid esters enumerated above are

methyl dimethylphosphinate, ethyl diethylphosphinate, n-propyldi-n-propylphosphinate, n-butyl di-n-butylphosphinate, methyldiethylphosphinate, ethyl dimethylphosphinate, perfluoromethylbisperfluoromethylphosphinate,(2,2,2-trifluoroethyl)bis(2,2,2-trifluoroethyl)phosphonate,perfluoroethyl bisperfluoroethylphosphinate, methylbisperfluoromethylphosphinate, methylbis(2,2,2-trifluoroethyl)phosphinate, methylbisperfluoroethylphosphinate, ethyl bisperfluoromethylphosphinate, ethylbis(2,2,2-trifluoroethyl)phosphinate, ethylbisperfluoroethylphosphinate, (2,2,2-trifluoroethyl)dimethylphosphinate,(2,2,2-trifluoroethyl) diethylphosphinate, and the like.

Examples of the compound in which all of R¹, R², and R³ are alkyl groupsinclude

trimethylphosphine oxide, triethylphosphine oxide, tri-n-propylphosphineoxide, triisopropylphosphine oxide, tri-n-butylphosphine oxide,triisobutylphosphine oxide, tri-tert-butylphosphine oxide,tricyclopentylphosphine oxide, tricyclohexylphosphine oxide,ethyldimethylphosphine oxide, dimethyl-n-propylphosphine oxide,isopropyldimethylphosphine oxide, n-butyldimethylphosphine oxide,isobutyldimethylphosphine oxide, tert-butyldimethylphosphine oxide,cyclopentyldimethylphosphine oxide, cyclohexyldimethylphosphine oxide,diethylmethylphosphine oxide, diethyl-n-propylphosphine oxide,diethyl-n-butylphosphine oxide, cyclohexyldiethylphosphine oxide,methyldi-n-propylphosphine oxide, ethyldi-n-propylphosphine oxide,cyclohexyldi-n-propylphosphine oxide, di-n-butylmethylphosphine oxide,di-n-butylethylphosphine oxide, di-n-butylcyclohexylphosphine oxide,dicyclohexylmethylphosphine oxide, dicyclohexylethylphosphine oxide,dicyclohexyl-n-propylphosphine oxide, n-butyldicyclohexylphosphineoxide, ethylmethyl-n-propylphosphine oxide,ethylmethylisopropylphosphine oxide, ethylmethyl-n-butylphosphine oxide,ethylmethylisobutylphosphine oxide, ethylmethyl-tert-butylphosphineoxide, ethylmethylcyclopentylphosphine oxide,ethylmethylcyclohexylphosphine oxide, n-butylmethyl-n-propylphosphineoxide, n-butylmethylcyclohexylphosphine oxide,cyclohexylmethyl(2,2,2-trifluoroethyl)phosphine oxide,triperfluoromethylphosphine oxide, tri(2,2,2-trifluoroethyl)phosphineoxide, triperfluoroethylphosphine oxide,tri(2-fluorocyclohexyl)phosphine oxide, tri(3-fluorocyclohexyl)phosphineoxide, tri(4-fluorocyclohexyl)phosphine oxide,perfluoromethyldimethylphosphine oxide,(2,2,2-trifluoroethyl)dimethylphosphine oxide,perfluoroethyldimethylphosphine oxide,(2-fluorocyclohexyl)dimethylphosphine oxide,(3-fluorocyclohexyl)dimethylphosphine oxide,(4-fluorocyclohexyl)dimethylphosphine oxide,diethyl(2,2,2-trifluoroethyl)phosphine oxide,di-n-butyl(2,2,2-trifluoroethyl)phosphine oxide,dicyclohexyl(2,2,2-trifluoroethyl)phosphine oxide,di(2,2,2-trifluoroethyl)methylphosphine oxide,ethylbis(2,2,2-trifluoroethyl)phosphine oxide,n-butyldi(2,2,2-trifluoroethyl)phosphine oxide,cyclohexyldi(2,2,2-trifluoroethyl)phosphine oxide,ethylmethylperfluoromethylphosphine oxide,ethylmethyl(2,2,2-trifluoroethyl)phosphine oxide,ethylmethylperfluoroethylphosphine oxide,ethylmethyl(2-fluorocyclohexyl)phosphine oxide,ethylmethyl(3-fluorocyclohexyl)phosphine oxide,ethylmethyl(4-fluorocyclohexyl)phosphine oxide,n-butylmethyl(2,2,2-trifluoroethyl)phosphine oxide,n-butylethyl-n-propylphosphine oxide, n-butylethylcyclohexylphosphineoxide, n-butylethyl(2,2,2-trifluoroethyl)phosphine oxide,cyclohexylethyl(2,2,2-trifluoroethyl)phosphine oxide, andn-butylcyclohexyl(2,2,2-trifluoroethyl)phosphine oxide, and the like.

Preferred of the phosphine oxides enumerated above are

trimethylphosphine oxide, triethylphosphine oxide, tri-n-propylphosphineoxide, tri-n-butylphosphine oxide, ethyldimethylphosphine oxide,diethylmethylphosphine oxide, triperfluoromethylphosphine oxide,tri(2,2,2-trifluoroethyl)phosphine oxide, triperfluoroethylphosphineoxide, and the like.

Examples of the compound in which any one of R¹, R², and R³ is afluorine atom include

dimethyl fluorophosphate, ethyl methyl fluorophosphate, methyl n-propylfluorophosphate, n-butyl methyl fluorophosphate, diethylfluorophosphate, ethyl n-propyl fluorophosphate, n-butyl ethylfluorophosphate, di-n-propyl fluorophosphate, n-butyl n-propylfluorophosphate, di-n-butyl fluorophosphate, cyclopentyl methylfluorophosphate, cyclopentyl ethyl fluorophosphate, cyclopentyl n-propylfluorophosphate, cyclopentyl n-butyl fluorophosphate, dicyclopentylfluorophosphate, cyclohexyl methyl fluorophosphate, cyclohexyl ethylfluorophosphate, cyclohexyl n-propyl fluorophosphate, cyclohexyl n-butylfluorophosphate, dicyclohexyl fluorophosphate,bis(trifluoromethyl)fluorophosphate,methyl(trifluoromethyl)fluorophosphate,ethyl(trifluoromethyl)fluorophosphate,n-propyl(trifluoromethyl)fluorophosphate,bis(2,2,2-trifluoroethyl)fluorophosphate,methyl(2,2,2-trifluoroethyl)fluorophosphate,ethyl(2,2,2-trifluoroethyl)fluorophosphate,n-propyl(2,2,2-trifluoroethyl)fluorophosphate, (2,2,2-trifluoroethyl)(trifluoromethyl)fluorophosphate, bis(pentafluoroethyl)fluorophosphate,methyl(pentafluoroethyl)fluorophosphate,ethyl(pentafluoroethyl)fluorophosphate,n-propyl(pentafluoroethyl)fluorophosphate, (pentafluoroethyl)(trifluoromethyl)fluorophosphate, and (pentafluoroethyl)(2,2,2-trifluoroethyl)fluorophosphate and the like.

Preferred of the monofluorophosphoric acid esters enumerated above are

dimethyl fluorophosphate, ethyl methyl fluorophosphate, methyl n-propylfluorophosphate, diethyl fluorophosphate, ethyl n-propylfluorophosphate, di-n-propyl fluorophosphate, bis(trifluoromethyl)fluorophosphate, methyl(trifluoromethyl) fluorophosphate,ethyl(trifluoromethyl) fluorophosphate, n-propyl(trifluoromethyl)fluorophosphate, bis(2,2,2-trifluoroethyl) fluorophosphate,methyl(2,2,2-trifluoroethyl) fluorophosphate,ethyl(2,2,2-trifluoroethyl) fluorophosphate,n-propyl(2,2,2-trifluoroethyl) fluorophosphate, bis(pentafluoroethyl)fluorophosphate, methyl(pentafluoroethyl) fluorophosphate,ethyl(pentafluoroethyl) fluorophosphate, n-propyl(pentafluoroethyl)fluorophosphate, and the like.

Examples of the compound in which any two of R¹, R², and R³ are fluorineatoms include

methyl difluorophosphate, ethyl difluorophosphate, n-propyldifluorophosphate, n-butyl difluorophosphate, cyclopentyldifluorophosphate, cyclohexyl difluorophosphate,(trifluoromethyl)difluorophosphate,(2,2,2-trifluoroethyl)difluorophosphate, and(pentafluoroethyl)difluorophosphate, and the like.<1-2-2. Nitrile Compounds>

The nitrile compounds are not particularly limited in the kind thereofso long as they are compounds having a nitrile group in the molecule.The nitrile compounds may be compounds each having two or more nitrilegroups per molecule. Examples of the nitrile compounds include

mono-nitrile compounds such as acetonitrile, propionitrile,butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile,2-methylbutyronitrile, trimethylacetonitrile, hexanenitrile,cyclopentanecarbonitrile, cyclohexanecarbonitrile, acrylonitrile,methacrylonitrile, crotononitrile, 3-methylcrotononitrile,2-methyl-2-butenenitrile, 2-pentenenitrile, 2-methyl-2-pentenenitrile,3-methyl-2-pentenenitrile, 2-hexenenitrile, fluoroacetonitrile,difluoroacetonitrile, trifluoroacetonitrile, 2-fluoropropionitrile,3-fluoropropionitrile, 2,2-difluoropropionitrile,2,3-difluoropropionitrile, 3,3-difluoropropionitrile,2,2,3-trifluoropropionitrile, 3,3,3-trifluoropropionitrile, andpentafluoropropionitrile, and the like;di-nitrile compounds such as malononitrile, succinonitrile,2-methylsuccinonitrile, tetramethylsuccinonitrile, glutaronitrile,2-methylglutaronitrile, adiponitrile, fumaronitrile, and2-methyleneglutaronitrile, and the like; andtetra-nitrile compounds such as tetracyanoethylene, and the like.

Preferred of these are

acetonitrile, propionitrile, butyronitrile, valeronitrile,crotononitrile, 3-methylcrotononitrile, malononitrile, succinonitrile,glutaronitrile, adiponitrile, fumaronitrile, and the like.

<1-2-3. Isocyanate Compounds>

The isocyanate compounds are not particularly limited in the kindthereof so long as they are compounds having an isocyanate group in themolecule. The isocyanate compounds may be compounds each having two ormore isocyanate groups per molecule. Examples of the isocyanatecompounds include monoisocyanate compounds such as methyl isocyanate,ethyl isocyanate, n-propyl isocyanate, isopropyl isocyanate, n-butylisocyanate, t-butyl isocyanate, cyclopentyl isocyanate, cyclohexylisocyanate, phenyl isocyanate, vinyl isocyanate, and allyl isocyanate,and the like;

diisocyanate compounds such as methane diisocyanate, 1,2-ethanediisocyanate, 1,3-propane diisocyanate, and 1,4-dicyanatobutane and thelike;

ester-group-containing isocyanate compounds such as methylisocyanatoformate, ethyl isocyanatoformate, methyl isocyanatoacetate,ethyl isocyanatoacetate, n-propyl isocyanatoacetate, methyl3-isocyanatopropionate, ethyl 3-isocyanatopropionate, n-propyl3-isocyanatopropionate, methyl 2-isocyanatopropionate, ethyl2-isocyanatopropionate, and n-propyl 2-isocyanatopropionate, and thelike;silicon-containing isocyanate compounds such asisocyanatotrimethylsilane, isocyanatotriethylsilane,isocyanatotri-n-propylsilane, isocyanatotrimethoxysilane,isocyanatotriethoxysilane, isocyanatotri-n-propoxysilane,isocyanatomethyltrimethylsilane, isocyanatomethyltriethylsilane,2-isocyanatoethyltrimethylsilane, 2-isocyanatoethyltriethylsilane,3-isocyanatopropyltrimethylsilane, 3-isocyanatopropyltriethylsilane,isocyanatomethyltrimethoxysilane, isocyanatomethyltriethoxysilane,2-isocyanatoethyltrimethoxysilane, 2-isocyanatoethyltriethoxysilane,3-isocyanatopropyltrimethoxysilane, and3-isocyanatopropyltriethoxysilane, and the like; andphosphorus-containing isocyanate compounds such as isocyanatodimethylphosphate, isocyanatoethyl methyl phosphate, isocyanatomethyl n-propylphosphate, isocyanato-n-butyl methyl phosphate, isocyanatodiethylphosphate, isocyanatoethyl n-propyl phosphate, isocyanato-n-butyl ethylphosphate, isocyanatodi-n-propyl phosphate, isocyanato-n-butyl n-propylphosphate, and isocyanatodi-n-butyl methyl phosphate, and the like.

Preferred of these are

methyl isocyanate, ethyl isocyanate, n-propyl isocyanate, n-butylisocyanate, methane diisocyanate, 1,2-ethane diisocyanate, 1,3-propanediisocyanate, 1,4-dicyanatobutane, methyl isocyanatoformate, ethylisocyanatoformate, methyl isocyanatoacetate, ethyl isocyanatoacetate,isocyanatotrimethylsilane, isocyanatotriethylsilane,isocyanatotri-n-propylsilane, isocyanatotrimethoxysilane,isocyanatotriethoxysilane, isocyanatotri-n-propoxysilane,isocyanatodimethyl phosphate, isocyanatoethyl methyl phosphate,isocyanatodiethyl phosphate, and the like.<1-2-4. Phosphazene Compounds>

The term “phosphazene compounds” in invention 3 means compounds having astructural unit represented by —PX^(a)X^(b)═N-(wherein X^(a) and X^(b)each independently represent a monovalent substituent). By the number ofsuch structural units and by the state in which the structural units arebonded, phosphazene compounds are classified into: monophosphazenesconstituted of only one structural unit of that kind; cyclicphosphazenes constituted of structural units of that kind which havebeen bonded cyclicly; polyphosphazenes constituted of structural unitsof that kind which have been bonded in an acyclic arrangement; etc. Thekinds of phosphazene compounds are not particularly limited, and acompound falling under any of these groups can be used. However, it ispreferred to use, among those compounds, a cyclic phosphazenerepresented by the following general formula (6) and/or an acyclicphosphazene represented by the following general formula (7).

[In general formula (6), X¹¹ and X¹² each independently represent amonovalent substituent.]

[In general formula (7), X²¹, X²², X²³, X²⁴, X²⁵, X²⁶, and X²⁷ eachindependently represent a monovalent substituent.]

In the following statement, when X¹¹, X¹², X²¹, X²², X²³, X²⁴, X²⁵, X²⁶,and X²⁷ are referred to without being especially distinguished from eachother, “X” is used for representing these.

The monovalent substituents are not particularly limited unless thesubstituents are counter to the spirit of invention 3. Examples thereofinclude halogen atoms, alkyl groups, aryl groups, acyl groups, carboxygroup, and groups represented by R—O— (wherein R represents an alkylgroup or an aryl group) (hereinafter suitably referred to as “ROgroups”). Of these, halogen atoms or RO groups are preferred from thestandpoint of electrochemical stability.

The halogen atoms preferably are fluorine, chlorine, and bromine atoms.Especially preferred is a fluorine atom. On the other hand, with respectto the RO groups, when R is an alkyl group, preferred examples of R arealkyl groups having 1-6 carbon atoms. Specific examples of suchpreferred alkyl groups represented by R include methyl, ethyl, n-propyl,and isopropyl. Especially preferred is methyl or ethyl. On the otherhand, when R is an aryl group, preferred examples thereof includephenyl, tolyl, and naphthyl. Especially preferred is phenyl.Incidentally, the hydrogen atoms possessed by the alkyl group or arylgroup represented by R may have been replaced with halogen atoms.Replacement with fluorine is especially preferred because this enhanceselectrochemical stability. Although all the substituents represented byX may be of the same kind, the substituents may be a combination ofsubstituents of two or more different kinds.

In general formula (6), n represents an integer of generally from 3 to10, preferably 5 or smaller. In general formula (7), m represents aninteger which is generally 0 or larger, and is generally 10 or smaller,preferably 3 or smaller. When n or m exceeds 10, there are cases whereincorporation of these compounds into an electrolyte results in anincrease in viscosity and hence in a decrease in conductivity and thisreduces battery performances including load characteristics.

The molecular weights of the compounds respectively represented bygeneral formula (6) and general formula (7) each are generally in therange of from 200 to 2,000, preferably to 1,000. When the molecularweights thereof are too high, there are cases where a dissolutionfailure occurs or an increase in higher viscosity results to impair loadcharacteristics.

<1-2-5. Disulfonic Acid Ester Compounds>

The disulfonic acid ester compounds are not particularly limited in thekind thereof so long as they are compounds having two sulfonic acidester structures in the molecule. Examples of acyclic disulfonic acidesters include

ethanediol disulfonates such as ethanediol dimethanesulfonate,ethanediol diethanesulfonate, ethanediol dipropanesulfonate, ethanedioldibutanesulfonate, ethanediol bis(trifluoromethanesulfonate), ethanediolbis(pentafluoroethanesulfonate), ethanediolbis(heptafluoropropanesulfonate), ethanediolbis(perfluorobutanesulfonate), ethanediolbis(perfluoropentanesulfonate), ethanediolbis(perfluorohexanesulfonate), ethanediol bis(perfluorooctanesulfonate),ethanediol bis(perfluoro-1-methylethanesulfonate), ethanediolbis(perfluoro-1,1-dimethylethanesulfonate), ethanediolbis(perfluoro-3-methylbutanesulfonate), ethanedioldi(fluoromethanesulfonate), ethanediol bis(difluoromethanesulfonate),ethanediol di(2-fluoroethanesulfonate), ethanediolbis(1,1-difluoroethanesulfonate), ethanediolbis(1,2-difluoroethanesulfonate), ethanediolbis(2,2-difluoroethanesulfonate), ethanediolbis(1,1,2-trifluoroethanesulfonate), ethanediolbis(1,2,2-trifluoroethanesulfonate), ethanediolbis(2,2,2-trifluoroethanesulfonate), ethanediolbis(1,1,2,2-tetrafluoroethanesulfonate), ethanediolbis(1,2,2,2-tetrafluoroethanesulfonate), ethanedioldi(1-fluoro-1-methylethanesulfonate), ethanediolbis(1,2,2,2-tetrafluoro-1-methylethanesulfonate), ethanediolbis(1,1-difluoro-2-methylpropanesulfonate), ethanediolbis(1,2,2,3,3,3-hexafluoro-1-methylpropanesulfonate), ethanedioldi(2-fluoro-1-fluoromethylethanesulfonate), ethanediolbis(2,2,2-trifluoro-1-trifluoromethylethanesulfonate), ethanediolbis(1-trifluoromethylethanesulfonate), ethanedioldi(1-methyl-1-trifluoromethylethanesulfoante), and ethanediolbis(1-trifluoromethylhexanesulfonate), and the like;1,2-propanediol disulfonates such as 1,2-propanediol dimethanesulfonate,1,2-propanediol diethanesulfonate, 1,2-propanediol dipropanesulfonate,1,2-propanediol dibutanesulfonate, 1,2-propanediolbis(trifluoromethanesulfonate), 1,2-propanediolbis(pentafluoroethanesulfonate), 1,2-propanediolbis(heptafluoropropanesulfonate), 1,2-propanediolbis(perfluorobutanesulfonate), 1,2-propanediolbis(perfluoropentanesulfonate), 1,2-propanediolbis(perfluorohexanesulfonate), 1,2-propanediolbis(perfluorooctanesulfonate), 1,2-propanediolbis(perfluoro-1-methylethanesulfonate), 1,2-propanediolbis(perfluoro-1,1-dimethylethanesulfonate), 1,2-propanediolbis(perfluoro-3-methylbutanesulfonate), 1,2-propanedioldi(fluoromethanesulfonate), 1,2-propanediolbis(difluoromethanesulfonate), 1,2-propanedioldi(2-fluoroethanesulfonate), 1,2-propanediolbis(1,1-difluoroethanesulfonate), 1,2-propanediolbis(1,2-difluoroethanesulfonate), 1,2-propanediolbis(2,2-difluoroethanesulfonate), 1,2-propanediolbis(1,1,2-trifluoroethanesulfonate), 1,2-propanediolbis(1,2,2-trifluoroethanesulfonate), 1,2-propanediolbis(2,2,2-trifluoroethanesulfonate), 1,2-propanediolbis(1,1,2,2-tetrafluoroethanesulfonate), 1,2-propanediolbis(1,2,2,2-tetrafluoroethanesulfonate), 1,2-propanedioldi(1-fluoro-1-methylethanesulfonate), 1,2-propanediolbis(1,2,2,2-tetrafluoro-1-methylethanesulfonate), 1,2-propanediolbis(1,1-difluoro-2-methylpropanesulfonate), 1,2-propanediolbis(1,2,2,3,3,3-hexafluoro-1-methylpropanesulfonate), 1,2-propanedioldi(2-fluoro-1-fluoromethylethanesulfonate), 1,2-propanediolbis(2,2,2-trifluoro-1-trifluoromethylethanesulfonate), 1,2-propanediolbis(1-trifluoromethylethanesulfonate), 1,2-propanedioldi(1-methyl-1-trifluoromethylethanesulfoante), and 1,2-propanediolbis(1-trifluoromethylhexanesulfonate), and the like;1,3-propanediol disulfonates such as 1,3-propanediol dimethanesulfonate,1,3-propanediol diethanesulfonate, 1,3-propanediol dipropanesulfonate,1,3-propanediol dibutanesulfonate, 1,3-propanediolbis(trifluoromethanesulfonate), 1,3-propanediolbis(pentafluoroethanesulfonate), 1,3-propanediolbis(heptafluoropropanesulfonate), 1,3-propanediolbis(perfluorobutanesulfonate), 1,3-propanediolbis(perfluoropentanesulfonate), 1,3-propanediolbis(perfluorohexanesulfonate), 1,3-propanediolbis(perfluorooctanesulfonate), 1,3-propanediolbis(perfluoro-1-methylethanesulfonate), 1,3-propanediolbis(perfluoro-1,1-dimethylethanesulfonate), 1,3-propanediolbis(perfluoro-3-methylbutanesulfonate), 1,3-propanedioldi(fluoromethanesulfonate), 1,3-propanediolbis(difluoromethanesulfonate), 1,3-propanedioldi(2-fluoroethanesulfonate), 1,3-propanediolbis(1,1-difluoroethanesulfonate), 1,3-propanediolbis(1,2-difluoroethanesulfonate), 1,3-propanediolbis(2,2-difluoroethanesulfonate), 1,3-propanediolbis(1,1,2-trifluoroethanesulfonate), 1,3-propanediolbis(1,2,2-trifluoroethanesulfonate), 1,3-propanediolbis(2,2,2-trifluoroethanesulfonate), 1,3-propanediolbis(1,1,2,2-tetrafluoroethanesulfonate), 1,3-propanediolbis(1,2,2,2-tetrafluoroethanesulfonate), 1,3-propanedioldi(1-fluoro-1-methylethanesulfonate), 1,3-propanediolbis(1,2,2,2-tetrafluoro-1-methylethanesulfonate), 1,3-propanediolbis(1,1-difluoro-2-methylpropanesulfonate), 1,3-propanediolbis(1,2,2,3,3,3-hexafluoro-1-methylpropanesulfonate), 1,3-propanedioldi(2-fluoro-1-fluoromethylethanesulfonate), 1,3-propanediolbis(2,2,2-trifluoro-1-trifluoromethylethanesulfonate), 1,3-propanediolbis(1-trifluoromethylethanesulfonate), 1,3-propanedioldi(1-methyl-1-trifluoromethylethanesulfoante), and 1,3-propanediolbis(1-trifluoromethylhexanesulfonate);1,2-butanediol disulfonates such as 1,2-butanediol dimethanesulfonate,1,2-butanediol diethanesulfonate, 1,2-butanediolbis(trifluoromethanesulfonate), 1,2-butanediolbis(pentafluoroethanesulfonate), 1,2-butanediolbis(heptafluoropropanesulfonate), 1,2-butanediolbis(perfluorobutanesulfonate), 1,2-butanediolbis(perfluoro-1-methylethanesulfonate), 1,2-butanediolbis(perfluoro-1,1-dimethylethanesulfonate), 1,2-butanedioldi(fluoromethanesulfonate), 1,2-butanediolbis(difluoromethanesulfonate), 1,2-butanedioldi(2-fluoroethanesulfonate), 1,2-butanediolbis(2,2-difluoroethanesulfonate), 1,2-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,2-butanedioldi(1-fluoro-1-methylethanesulfonate), 1,2-butanedioldi(2-fluoro-1-fluoromethylethanesulfonate), 1,2-butanediolbis(2,2,2-trifluoro-1-trifluoromethylethanesulfonate), 1,2-butanediolbis(1-trifluoromethylethanesulfonate), 1,2-butanedioldi(1-methyl-1-trifluoromethylethanesulfonate), and 1,2-butanediolbis(1-trifluoromethylhexanesulfonate) and the like;1,3-butanediol disulfonates such as 1,3-butanediol dimethanesulfonate,1,3-butanediol diethanesulfonate, 1,3-butanediolbis(trifluoromethanesulfonate), 1,3-butanediolbis(pentafluoroethanesulfonate), 1,3-butanediolbis(heptafluoropropanesulfonate), 1,3-butanediolbis(perfluorobutanesulfonate), 1,3-butanediolbis(perfluoro-1-methylethanesulfonate), 1,3-butanediolbis(perfluoro-1,1-dimethylethanesulfonate), 1,3-butanedioldi(fluoromethanesulfonate), 1,3-butanediolbis(difluoromethanesulfonate), 1,3-butanedioldi(2-fluoroethanesulfonate), 1,3-butanediolbis(2,2-difluoroethanesulfonate), 1,3-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,3-butanedioldi(1-fluoro-1-methylethanesulfonate), 1,3-butanedioldi(2-fluoro-1-fluoromethylethanesulfonate), 1,3-butanediolbis(2,2,2-trifluoro-1-trifluoromethylethanesulfonate), 1,3-butanediolbis[(1-trifluoromethyl)ethanesulfonate], 1,3-butanedioldi(1-methyl-1-trifluoromethylethanesulfonate), and 1,3-butanediolbis(1-trifluoromethylhexanesulfonate) and the like;1,4-butanediol disulfonates such as 1,4-butanediol dimethanesulfonate,1,4-butanediol diethanesulfonate, 1,4-butanediol dipropanesulfonate,1,4-butanediol dibutanesulfonate, 1,4-butanediolbis(trifluoromethanesulfonate), 1,4-butanediolbis(pentafluoroethanesulfonate), 1,4-butanediolbis(heptafluoropropanesulfonate), 1,4-butanediolbis(perfluorobutanesulfonate), 1,4-butanediolbis(perfluoropentanesulfonate), 1,4-butanediolbis(perfluorohexanesulfonate), 1,4-butanediolbis(perfluorooctanesulfonate), 1,4-butanediolbis(perfluoro-1-methylethanesulfonate), 1,4-butanediolbis(perfluoro-1,1-dimethylethanesulfonate), 1,4-butanediolbis(perfluoro-3-methylbutanesulfonate), 1,4-butanedioldi(fluoromethanesulfonate), 1,4-butanediolbis(difluoromethanesulfonate), 1,4-butanedioldi(2-fluoroethanesulfonate), 1,4-butanediolbis(1,1-difluoroethanesulfonate), 1,4-butanediolbis(1,2-difluoroethanesulfonate), 1,4-butanediolbis(2,2-difluoroethanesulfonate), 1,4-butanediolbis(1,1,2-trifluoroethanesulfonate), 1,4-butanediolbis(1,2,2-trifluoroethanesulfonate), 1,4-butanediolbis(2,2,2-trifluoroethanesulfonate), 1,4-butanediolbis(1,1,2,2-tetrafluoroethanesulfonate), 1,4-butanediolbis(1,2,2,2-tetrafluoroethanesulfonate), 1,4-butanedioldi(1-fluoro-1-methylethanesulfonate), 1,4-butanediolbis(1,2,2,2-tetrafluoro-1-methylethanesulfonate), 1,4-butanediolbis(1,1-difluoro-2-methylpropanesulfonate), 1,4-butanediolbis(1,2,2,3,3,3-hexafluoro-1-methylpropanesulfonate), 1,4-butanedioldi(2-fluoro-1-fluoromethylethanesulfonate), 1,4-butanediolbis(2,2,2-trifluoro-1-trifluoromethylethanesulfonate), 1,4-butanediolbis(1-trifluoromethylethanesulfonate), 1,4-butanedioldi(1-methyl-1-trifluoromethylethanesulfoante), and 1,4-butanediolbis(1-trifluoromethylhexanesulfonate), and the like; and1,4-benzenediol disulfonates such as 1,4-benzenediol dimethanesulfonate,1,4-benzenediol diethanesulfonate, 1,4-benzenediolbis(trifluoromethanesulfonate), 1,4-benzenediolbis(pentafluoroethanesulfonate), 1,4-benzenediolbis(heptafluoropropanesulfonate), 1,4-benzenediolbis(perfluorobutanesulfonate), 1,4-benzenediolbis(perfluoro-1-methylethanesulfonate), 1,4-benzenediolbis(perfluoro-1,1-dimethylethanesulfonate), 1,4-benzenedioldi(fluoromethanesulfonate), 1,4-benzenediol di(2-fluoroethanesulfonate),1,4-benzenediol bis(2,2-difluoroethanesulfonate), 1,4-benzenediolbis(2,2,2-trifluoroethanesulfonate), 1,4-benzenedioldi(1-fluoro-1-methylethanesulfonate), 1,4-benzenedioldi(2-fluoro-1-fluoromethylethanesulfonate), 1,4-benzenediolbis(2,2,2-trifluoro-1-trifluoromethylethanesulfonate), 1,4-benzenediolbis(1-trifluoromethylethanesulfonate), 1,4-benzenedioldi(1-methyl-1-trifluoromethylethanesulfonate), and 1,4-benzenediolbis(1-trifluoromethylhexanesulfonate) and the like.

Preferred of these are

ethanediol disulfonates such as ethanediol dimethanesulfonate,ethanediol diethanesulfonate, ethanediol bis(trifluoromethanesulfonate),ethanediol bis(pentafluoroethanesulfonate), ethanedioldi(fluoromethanesulfonate), ethanediol bis(difluoromethanesulfonate),ethanediol di(2-fluoroethanesulfonate), ethanediolbis(2,2-difluoroethanesulfonate), and ethanediolbis(2,2,2-trifluoroethanesulfonate) and the like;1,2-propanediol disulfonates such as 1,2-propanediol dimethanesulfonate,1,2-propanediol diethanesulfonate, 1,2-propanediolbis(trifluoromethanesulfonate), 1,2-propanediolbis(pentafluoroethanesulfonate), 1,2-propanedioldi(fluoromethanesulfonate), 1,2-propanediolbis(difluoromethanesulfonate), 1,2-propanedioldi(2-fluoroethanesulfonate), 1,2-propanediolbis(2,2-difluoroethanesulfonate), and 1,2-propanediolbis(2,2,2-trifluoroethanesulfonate), and the like;1,3-propanediol disulfonates such as 1,3-propanediol dimethanesulfonate,1,3-propanediol diethanesulfonate, 1,3-propanediolbis(trifluoromethanesulfonate), 1,3-propanediolbis(pentafluoroethanesulfonate), 1,3-propanedioldi(fluoromethanesulfonate), 1,3-propanediolbis(difluoromethanesulfonate), 1,3-propanedioldi(2-fluoroethanesulfonate), 1,3-propanediolbis(2,2-difluoroethanesulfonate), and 1,3-propanediolbis(2,2,2-trifluoroethanesulfonate) and the like;1,2-butanediol disulfonates such as 1,2-butanediol dimethanesulfonate,1,2-butanediol diethanesulfonate, 1,2-butanediolbis(trifluoromethanesulfonate), 1,2-butanediolbis(pentafluoroethanesulfonate), 1,2-butanedioldi(fluoromethanesulfonate), 1,2-butanediolbis(difluoromethanesulfonate), 1,2-butanedioldi(2-fluoroethanesulfonate), 1,2-butanediolbis(2,2-difluoroethanesulfonate), and 1,2-butanediolbis(2,2,2-trifluoroethanesulfonate) and the like;1,3-butanediol disulfonates such as 1,3-butanediol dimethanesulfonate,1,3-butanediol diethanesulfonate, 1,3-butanediolbis(trifluoromethanesulfonate), 1,3-butanediolbis(pentafluoroethanesulfonate), 1,3-butanedioldi(fluoromethanesulfonate), 1,3-butanediolbis(difluoromethanesulfonate), 1,3-butanedioldi(2-fluoroethanesulfonate), 1,3-butanediolbis(2,2-difluoroethanesulfonate), and 1,3-butanediolbis(2,2,2-trifluoroethanesulfonate) and the like; and1,4-butanediol disulfonates such as 1,4-butanediol dimethanesulfonate,1,4-butanediol diethanesulfonate, 1,4-butanediolbis(trifluoromethanesulfonate), 1,4-butanediolbis(pentafluoroethanesulfonate), 1,4-butanedioldi(fluoromethanesulfonate), 1,4-butanediolbis(difluoromethanesulfonate), 1,4-butanedioldi(2-fluoroethanesulfonate), 1,4-butanediolbis(2,2-difluoroethanesulfonate), and 1,4-butanediolbis(2,2,2-trifluoroethanesulfonate) and the like.

Especially preferred of these are

ethanediol disulfonates such as ethanediolbis(trifluoromethanesulfonate), ethanediolbis(pentafluoroethanesulfonate), ethanediol di(fluoromethanesulfonate),ethanediol di(2-fluoroethanesulfonate), and ethanediolbis(2,2,2-trifluoroethanesulfonate) and the like;1,2-propanediol disulfonates such as 1,2-propanediolbis(trifluoromethanesulfonate), 1,2-propanediolbis(pentafluoroethanesulfonate), 1,2-propanedioldi(fluoromethanesulfonate), 1,2-propanediol di(2-fluoroethanesulfonate),and 1,2-propanediol bis(2,2,2-trifluoroethanesulfonate) and the like;1,3-propanediol disulfonates such as 1,3-propanediolbis(trifluoromethanesulfonate), 1,3-propanediolbis(pentafluoroethanesulfonate), 1,3-propanedioldi(2-fluoroethanesulfonate), and 1,3-propanediolbis(2,2,2-trifluoroethanesulfonate) and the like;1,2-butanediol disulfonates such as 1,2-butanediolbis(trifluoromethanesulfonate), 1,2-butanediolbis(pentafluoroethanesulfonate), 1,2-butanedioldi(fluoromethanesulfonate), 1,2-butanediol di(2-fluoroethanesulfonate),and 1,2-butanediol bis(2,2,2-trifluoroethanesulfonate) and the like;1,3-butanediol disulfonates such as 1,3-butanediolbis(trifluoromethanesulfonate), 1,3-butanediolbis(pentafluoroethanesulfonate), 1,3-butanedioldi(fluoromethanesulfonate), 1,3-butanediol di(2-fluoroethanesulfonate),and 1,3-butanediol bis(2,2,2-trifluoroethanesulfonate) and the like; and1,4-butanediol disulfonates such as 1,4-butanediolbis(trifluoromethanesulfonate), 1,4-butanediolbis(pentafluoroethanesulfonate), 1,4-butanedioldi(fluoromethanesulfonate), 1,4-butanediol di(2-fluoroethanesulfonate),and 1,4-butanediol bis(2,2,2-trifluoroethanesulfonate) and the like.

Examples of cyclic disulfonic acid esters include

1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3-methyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3-dimethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3-fluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3-difluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6-methyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6,6-dimethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6-fluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6,6-difluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,6-dimethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,6-difluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3,6,6-tetramethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3,6,6-tetrafluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3-methyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3-dimethyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3-fluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3-difluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,6-dimethyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,6-difluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3,6,6-tetramethyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3,6,6-tetrafluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,3-methyl-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,3,3-dimethyl-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,3-fluoro-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,3,3-difluoro-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,1,5,2,4-dioxadithiepane-2,2,4,4-tetraoxide,3-methyl-1,5,2,4-dioxadithiepane-2,2,4,4-tetraoxide,3,3-dimethyl-1,5,2,4-dioxadithiepane-2,2,4,4-tetraoxide,3-fluoro-1,5,2,4-dioxadithiepane-2,2,4,4-tetraoxide,3,3-difluoro-1,5,2,4-dioxadithiepane-2,2,4,4-tetraoxide,6-methyl-1,5,2,4-dioxadithiepane-2,2,4,4-tetraoxide,6,7-dimethyl-1,5,2,4-dioxadithiepane-2,2,4,4-tetraoxide,1,5,2,4-dioxadithiocane-2,2,4,4-tetraoxide, and1,5,2,4-dioxadithionane-2,2,4,4-tetraoxide, and the like.

Preferred are compounds having a six-membered ring structure such as

1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3-methyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3-dimethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3-fluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3-difluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6-methyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6,6-dimethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6-fluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,6,6-difluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,6-dimethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,6-difluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3,6,6-tetramethyl-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,3,3,6,6-tetrafluoro-1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide,1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3-methyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3-dimethyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3-fluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3-difluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,6-dimethyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,6-difluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3,6,6-tetramethyl-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,3,3,6,6-tetrafluoro-1,4,2,5-dioxadithiane-2,2,5,5-tetraoxide,1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,3-methyl-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,3,3-dimethyl-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide,3-fluoro-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide, and3,3-difluoro-1,5,2,4-dioxadithian-6-one-2,2,4,4-tetraoxide.<1-2-6. Sulfide Compounds>

The sulfide compounds are not particularly limited in the kind thereofso long as they are compounds having a sulfide structure in themolecule. Examples of the sulfide compounds include

dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, diisopropylsulfide, di-n-butyl sulfide, diisobutyl sulfide, di-tert-butyl sulfide,dicyclopentyl sulfide, dicyclohexyl sulfide,

ethyl methyl sulfide, methyl propyl sulfide, methyl isopropyl sulfide,methyl n-butyl sulfide, methyl isobutyl sulfide, methyl tert-butylsulfide, methyl cyclopentyl sulfide, methyl cyclohexyl sulfide, ethylpropyl sulfide, ethyl isopropyl sulfide, ethyl n-butyl sulfide, ethylisobutyl sulfide, ethyl tert-butyl sulfide, ethyl cyclopentyl sulfide,ethyl cyclohexyl sulfide,diphenyl sulfide, di(2-tolyl)sulfide, di(3-tolyl)sulfide,di(4-tolyl)sulfide, divinyl sulfide, diallyl sulfide, dibenzyl sulfide,methyl phenyl sulfide, methyl(2-tolyl)sulfide, methyl(3-tolyl)sulfide,methyl(4-tolyl)sulfide, methyl vinyl sulfide, methyl allyl sulfide,methyl benzyl sulfide, ethyl phenyl sulfide, ethyl(2-tolyl)sulfide,ethyl(3-tolyl)sulfide, ethyl(4-tolyl)sulfide, ethyl vinyl sulfide, ethylallyl sulfide, ethyl benzyl sulfide,phenyl propyl sulfide, phenyl isopropyl sulfide, phenyl n-butyl sulfide,phenyl isobutyl sulfide, phenyl tert-butyl sulfide, phenyl cyclopentylsulfide, phenyl cyclohexyl sulfide, phenyl(2-tolyl)sulfide,phenyl(3-tolyl)sulfide, phenyl(4-tolyl)sulfide, phenyl vinyl sulfide,phenyl allyl sulfide, phenyl benzyl sulfide,bis(fluoromethyl)sulfide, bis(difluoromethyl)sulfide,bis(trifluoromethyl)sulfide, di(1-fluoroethyl)sulfide,di(2-fluoroethyl)sulfide, bis(2,2,2-trifluoroethyl) sulfide,bis(perfluoroethyl)sulfide, bis(3,3,3-trifluoro-n-propyl)sulfide,bis(2,2,3,3,3-pentafluoro-n-propyl)sulfide,bis(perfluoro-n-propyl)sulfide, di(2-fluoroisopropyl)sulfide,bis(2,2,2,2′,2′,2′-hexafluoroisopropyl)sulfide,bis(perfluoro-n-butyl)sulfide, di(2-fluoro-tert-butyl)sulfide,bis(perfluoro-tert-butyl)sulfide, di(2-fluorocyclohexyl)sulfide,di(3-fluorocyclohexyl)sulfide, di(4-fluorocyclohexyl)sulfide,bis(perfluorocyclohexyl)sulfide, methyl(fluoromethyl)sulfide,methyl(difluoromethyl)sulfide, methyl(trifluoromethyl)sulfide,methyl(1-fluoroethyl)sulfide, methyl(2-fluoroethyl)sulfide,methyl(2,2,2-trifluoroethyl)sulfide, methyl(perfluoroethyl)sulfide,methyl(3,3,3-trifluoro-n-propyl sulfide),methyl(2,2,3,3,3-pentafluoro-n-propyl)sulfide, methyl perfluoro-n-propylsulfide, methyl(2-fluoroisopropyl)sulfide,methyl(2,2,2,2′,2′,2′-hexafluoroisopropyl)sulfide,methyl(perfluoro-n-butyl)sulfide, methyl(2-fluoro-tert-butyl)sulfide,methyl(perfluoro-tert-butyl) sulfide, methyl(2-fluorocyclohexyl)sulfide,methyl(3-fluorocyclohexyl)sulfide, methyl(4-fluorocyclohexyl)sulfide,methyl(perfluorocyclohexyl)sulfide,ethyl(fluoromethyl)sulfide, ethyl(difluoromethyl)sulfide,ethyl(trifluoromethyl)sulfide, ethyl(1-fluoroethyl)sulfide,ethyl(2-fluoroethyl)sulfide, ethyl(2,2,2-trifluoroethyl)sulfide,ethyl(perfluoroethyl)sulfide, ethyl(3,3,3-trifluoro-n-propyl)sulfide,ethyl(2,2,3,3,3-pentafluoro-n-propyl)sulfide,ethyl(perfluoro-n-propyl)sulfide, ethyl(2-fluoroisopropyl)sulfide, ethyl(2,2,2,2′,2′,2′-hexafluoroisopropyl)sulfide,ethyl(perfluoro-n-butyl)sulfide, ethyl(2-fluoro-tert-butyl)sulfide,ethyl(perfluoro-tert-butyl)sulfide, ethyl(2-fluorocyclohexyl)sulfide,ethyl(3-fluorocyclohexyl)sulfide, ethyl(4-fluorocyclohexyl)sulfide,ethyl(perfluorocyclohexyl)sulfide,(2,2,2-trifluoroethyl) (fluoromethyl)sulfide, (2,2,2-trifluoroethyl)(difluoromethyl)sulfide, (2,2,2-trifluoroethyl)(trifluoromethyl)sulfide, (2,2,2-trifluoroethyl) (1-fluoroethyl)sulfide,(2,2,2-trifluoroethyl) (2-fluoroethyl)sulfide, (2,2,2-trifluoroethyl)(perfluoroethyl)sulfide, (2,2,2-trifluoroethyl)(3,3,3-trifluoro-n-propyl)sulfide, (2,2,2-trifluoroethyl)(2,2,3,3,3-pentafluoro-n-propyl)sulfide, (2,2,2-trifluoroethyl)(perfluoro-n-propyl)sulfide, (2,2,2-trifluoroethyl)(2-fluoroisopropyl)sulfide, (2,2,2-trifluoroethyl)(2,2,2,2′,2′,2′-hexafluoroisopropyl)sulfide, (2,2,2-trifluoroethyl)(perfluoro-n-butyl)sulfide, (2,2,2-trifluoroethyl)(2-fluoro-tert-butyl)sulfide, (2,2,2-trifluoroethyl)(perfluoro-tert-butyl)sulfide, (2,2,2-trifluoroethyl)(2-fluorocyclohexyl)sulfide, (2,2,2-trifluoroethyl)(3-fluorocyclohexyl)sulfide, (2,2,2-trifluoroethyl)(4-fluorocyclohexyl)sulfide, (2,2,2-trifluoroethyl)(perfluorocyclohexyl)sulfide,di(2-fluorophenyl)sulfide, di(3-fluorophenyl)sulfide,di(4-fluorophenyl)sulfide, bis(2,3-difluorophenyl)sulfide,bis(2,4-difluorophenyl)sulfide, bis(3,5-difluorophenyl)sulfide,bis(2,4,6-trifluorophenyl)sulfide, bis(perfluorophenyl)sulfide,di(1-fluorovinyl)sulfide, di(2-fluorovinyl)sulfide,bis(perfluorovinyl)sulfide, bis[(2-fluorophenyl)methyl]sulfide,bis[(3-fluorophenyl)methyl]sulfide, bis[(4-fluorophenyl)methyl]sulfide,bis[(perfluorophenyl)methyl]sulfide,methyl(2-fluorophenyl)sulfide, methyl(3-fluorophenyl)sulfide,methyl(4-fluorophenyl)sulfide, methyl(2,3-difluorophenyl)sulfide,methyl(2,4-difluorophenyl)sulfide, methyl(3,5-difluorophenyl)sulfide,methyl(2,4,6-trifluorophenyl)sulfide, methyl(perfluorophenyl)sulfide,methyl(1-fluorovinyl)sulfide, methyl(2-fluorovinyl)sulfide, methylperfluorovinyl sulfide, methyl[(2-fluorophenyl)methyl]sulfide,methyl[(3-fluorophenyl)methyl]sulfide,methyl[(4-fluorophenyl)methyl]sulfide,methyl[(perfluorophenyl)methyl]sulfide,ethyl(2-fluorophenyl)sulfide, ethyl(3-fluorophenyl)sulfide,ethyl(4-fluorophenyl)sulfide, ethyl(2,3-difluorophenyl)sulfide,ethyl(2,4-difluorophenyl)sulfide, ethyl(3,5-difluorophenyl)sulfide,ethyl(2,4,6-trifluorophenyl)sulfide, ethyl(perfluorophenyl)sulfide,ethyl(1-fluorovinyl)sulfide, ethyl(2-fluorovinyl)sulfide,ethyl(perfluorovinyl)sulfide, ethyl[(2-fluorophenyl)ethyl]sulfide,ethyl[(3-fluorophenyl)ethyl]sulfide,ethyl[(4-fluorophenyl)methyl]sulfide,ethyl[(perfluorophenyl)methyl]sulfide,phenyl(fluoromethyl)sulfide, phenyl(difluoromethyl)sulfide,phenyl(trifluoromethyl)sulfide, phenyl(1-fluoroethyl)sulfide,phenyl(2-fluoroethyl)sulfide, phenyl(2,2,2-trifluoroethyl)sulfide,phenyl(perfluoroethyl)sulfide, phenyl(3,3,3-trifluoro-n-propyl) sulfide,phenyl(2,2,3,3,3-pentafluoro-n-propyl)sulfide,phenyl(perfluoro-n-propyl)sulfide, phenyl(2-fluoroisopropyl)sulfide,phenyl(2,2,2,2′,2′,2′-hexafluoroisopropyl)sulfide,phenyl(perfluoro-n-butyl)sulfide, phenyl(2-fluoro-tert-butyl)sulfide,phenyl(perfluoro-tert-butyl)sulfide, phenyl(2-fluorocyclohexyl)sulfide,phenyl(3-fluorocyclohexyl)sulfide, phenyl(4-fluorocyclohexyl)sulfide,phenyl(perfluorocyclohexyl)sulfide, phenyl(2-fluorophenyl)sulfide,phenyl(3-fluorophenyl)sulfide, phenyl(4-fluorophenyl)sulfide,phenyl(2,3-difluorophenyl)sulfide, phenyl(2,4-difluorophenyl)sulfide,phenyl(3,5-difluorophenyl)sulfide, phenyl(2,4,6-trifluorophenyl)sulfide,phenyl(perfluorophenyl)sulfide, phenyl(1-fluorovinyl)sulfide,phenyl(2-fluorovinyl)sulfide, phenyl(perfluorovinyl)sulfide,phenyl(2-fluorophenyl)methyl sulfide,phenyl[(3-fluorophenyl)methyl]sulfide,phenyl[(4-fluorophenyl)methyl]sulfide,phenyl[(perfluorophenyl)methyl]sulfide,(2,2,2-trifluoroethyl) (2-fluorophenyl)sulfide, (2,2,2-trifluoroethyl)(3-fluorophenyl)sulfide, (2,2,2-trifluoroethyl) (4-fluorophenyl)sulfide,(2,2,2-trifluoroethyl) (2,3-difluorophenyl)sulfide,(2,2,2-trifluoroethyl) (2,4-difluorophenyl)sulfide,(2,2,2-trifluoroethyl) (3,5-difluorophenyl)sulfide,(2,2,2-trifluoroethyl) (2,4,6-trifluorophenyl)sulfide,(2,2,2-trifluoroethyl) (perfluorophenyl)sulfide, (2,2,2-trifluoroethyl)(1-fluorovinyl)sulfide, (2,2,2-trifluoroethyl) (2-fluorovinyl)sulfide,(2,2,2-trifluoroethyl) (perfluorovinyl)sulfide, (2,2,2-trifluoroethyl)[(2-fluorophenyl)methyl]sulfide, (2,2,2-trifluoroethyl)[(3-fluorophenyl)methyl]sulfide, (2,2,2-trifluoroethyl)[(4-fluorophenyl)methyl]sulfide, and (2,2,2-trifluoroethyl)[(perfluorophenyl)methyl]sulfide and the like.<1-2-7. Disulfide Compounds>

The disulfide compounds are not particularly limited in the kind thereofso long as they are compounds having a disulfide structure in themolecule. Examples of the disulfide compounds include

dimethyl disulfide, diethyl disulfide, di-n-propyl disulfide,diisopropyl disulfide, di-n-butyl disulfide, diisobutyl disulfide,di-tert-butyl disulfide, dicyclopentyl disulfide, dicyclohexyldisulfide,

ethyl methyl disulfide, methyl propyl disulfide, methyl isopropyldisulfide, methyl n-butyl disulfide, methyl isobutyl disulfide, methyltert-butyl disulfide, methyl cyclopentyl disulfide, methyl cyclohexyldisulfide, ethyl propyl disulfide, ethyl isopropyl disulfide, ethyln-butyl disulfide, ethyl isobutyl disulfide, ethyl tert-butyl disulfide,ethyl cyclopentyl disulfide, ethyl cyclohexyl disulfide,diphenyl disulfide, di(2-tolyl)disulfide, di(3-tolyl)disulfide,di(4-tolyl)disulfide, divinyl disulfide, diallyl disulfide, dibenzyldisulfide,methyl phenyl disulfide, methyl(2-tolyl)disulfide,methyl(3-tolyl)disulfide, methyl(4-tolyl)disulfide, methyl vinyldisulfide, methyl allyl disulfide, methyl benzyl disulfide, ethyl phenyldisulfide, ethyl(2-tolyl) disulfide, ethyl(3-tolyl)disulfide,ethyl(4-tolyl)disulfide, ethyl vinyl disulfide, ethyl allyl disulfide,ethyl benzyl disulfide,phenyl propyl disulfide, phenyl isopropyl disulfide, phenyl n-butyldisulfide, phenyl isobutyl disulfide, phenyl tert-butyl disulfide,phenyl cyclopentyl disulfide, phenyl cyclohexyl disulfide,phenyl(2-tolyl)disulfide, phenyl(3-tolyl)disulfide,phenyl(4-tolyl)disulfide, phenyl vinyl disulfide, phenyl allyldisulfide, phenyl benzyl disulfide,bis(fluoromethyl)disulfide, bis(difluoromethyl)disulfide,bis(trifluoromethyl)disulfide, di(1-fluoroethyl)disulfide,di(2-fluoroethyl)disulfide, bis(2,2,2-trifluoroethyl)disulfide,bis(perfluoroethyl)disulfide, bis(3,3,3-trifluoro-n-propyl)disulfide,bis(2,2,3,3,3-pentafluoro-n-propyl)disulfide,bis(perfluoro-n-propyl)disulfide, di(2-fluoroisopropyl)disulfide,bis(2,2,2,2′,2′,2′-hexafluoroisopropyl)disulfide,bis(perfluoro-n-butyl)disulfide, di(2-fluoro-tert-butyl)disulfide,bis(perfluoro-tert-butyl)disulfide, di(2-fluorocyclohexyl)disulfide,di(3-fluorocyclohexyl)disulfide, di(4-fluorocyclohexyl)disulfide,bis(perfluorocyclohexyl)disulfide,methyl(fluoromethyl)disulfide, methyl(difluoromethyl)disulfide,methyl(trifluoromethyl)disulfide, methyl(1-fluoroethyl)disulfide,methyl(2-fluoroethyl)disulfide, methyl(2,2,2-trifluoroethyl)disulfide,methyl(perfluoroethyl)disulfide,methyl(3,3,3-trifluoro-n-propyl)disulfide,methyl(2,2,3,3,3-pentafluoro-n-propyl) disulfide,methyl(perfluoro-n-propyl)disulfide, methyl(2-fluoroisopropyl)disulfide,methyl(2,2,2,2′,2′,2′-hexafluoroisopropyl)disulfide,methyl(perfluoro-n-butyl)disulfide,methyl(2-fluoro-tert-butyl)disulfide,methyl(perfluoro-tert-butyl)disulfide,methyl(2-fluorocyclohexyl)disulfide, methyl(3-fluorocylohexyl)disulfide,methyl(4-fluorocyclohexyl)disulfide,methyl(perfluorocyclohexyl)disulfide,ethyl(fluoromethyl)disulfide, ethyl(difluoromethyl)disulfide,ethyl(trifluoromethyl)disulfide, ethyl(1-fluoroethyl)disulfide,ethyl(2-fluoroethyl)disulfide, ethyl(2,2,2-trifluoroethyl)disulfide,ethyl(perfluoroethyl)disulfide,ethyl(3,3,3-trifluoro-n-propyl)disulfide,ethyl(2,2,3,3,3-pentafluoro-n-propyl)disulfide,ethyl(perfluoro-n-propyl)disulfide, ethyl 2-fluoroisopropyl disulfide,ethyl(2,2,2,2′,2′,2′-hexafluoroisopropyl)disulfide,ethyl(perfluoro-n-butyl)disulfide, ethyl(2-fluoro-tert-butyl)disulfide,ethyl(perfluoro-tert-butyl)disulfide,ethyl(2-fluorocyclohexyl)disulfide, ethyl(3-fluorocylohexyl)disulfide,ethyl(4-fluorocyclohexyl)disulfide, ethyl(perfluorocyclohexyl)disulfide,(2,2,2-trifluoroethyl) (fluoromethyl)disulfide, (2,2,2-trifluoroethyl)(difluoromethyl)disulfide, (2,2,2-trifluoroethyl)(trifluoromethyl)disulfide, (2,2,2-trifluoroethyl)(1-fluoroethyl)disulfide, (2,2,2-trifluoroethyl)(2-fluoroethyl)disulfide, (2,2,2-trifluoroethyl)(perfluoroethyl)disulfide, (2,2,2-trifluoroethyl)(3,3,3-trifluoro-n-propyl)disulfide, (2,2,2-trifluoroethyl)(2,2,3,3,3-pentafluoro-n-propyl) disulfide, (2,2,2-trifluoroethyl)(perfluoro-n-propyl)disulfide, (2,2,2-trifluoroethyl)(2-fluoroisopropyl)disulfide, (2,2,2-trifluoroethyl)(2,2,2,2′,2′,2′-hexafluoroisopropyl)disulfide, (2,2,2-trifluoroethyl)(perfluoro-n-butyl)disulfide, (2,2,2-trifluoroethyl)(2-fluoro-tert-butyl)disulfide, (2,2,2-trifluoroethyl)(perfluoro-tert-butyl)disulfide, (2,2,2-trifluoroethyl)(2-fluorocyclohexyl)disulfide, (2,2,2-trifluoroethyl)(3-fluorocyclohexyl)disulfide, (2,2,2-trifluoroethyl)(4-fluorocyclohexyl)disulfide, (2,2,2-trifluoroethyl)(perfluorocyclohexyl)disulfide,di(2-fluorophenyl)disulfide, di(3-fluorophenyl)disulfide,di(4-fluorophenyl)disulfide, bis(2,3-difluorophenyl)disulfide,bis(2,4-difluorophenyl)disulfide, bis(3,5-difluorophenyl)disulfide,bis(2,4,6-trifluorophenyl)disulfide, bis(perfluorophenyl)disulfide,di(1-fluorovinyl)disulfide, di(2-fluorovinyl)disulfide,bis(perfluorovinyl)disulfide, bis[(2-fluorophenyl)methyl]disulfide,bis[(3-fluorophenyl)methyl]disulfide,bis[(4-fluorophenyl)methyl]disulfide,bis[(perfluorophenyl)methyl]disulfide,methyl(2-fluorophenyl)disulfide, methyl(3-fluorophenyl)disulfide,methyl(4-fluorophenyl)disulfide, methyl(2,3-difluorophenyl)disulfide,methyl(2,4-difluorophenyl)disulfide,methyl(3,5-difluorophenyl)disulfide,methyl(2,4,6-trifluorophenyl)disulfide,methyl(perfluorophenyl)disulfide, methyl(1-fluorovinyl)disulfide,methyl(2-fluorovinyl)disulfide, methyl(perfluorovinyl)disulfide,methyl[(2-fluorophenyl)methyl]disulfide,methyl[(3-fluorophenyl)methyl]disulfide,methyl[(4-fluorophenyl)methyl]disulfide,methyl[(perfluorophenyl)methyl]disulfide,ethyl(2-fluorophenyl)disulfide, ethyl(3-fluorophenyl)disulfide,ethyl(4-fluorophenyl)disulfide, ethyl(2,3-difluorophenyl)disulfide,ethyl(2,4-difluorophenyl)disulfide, ethyl(3,5-difluorophenyl)disulfide,ethyl(2,4,6-trifluorophenyl)disulfide, ethyl(perfluorophenyl)disulfide,ethyl(1-fluorovinyl)disulfide, ethyl(2-fluorovinyl)disulfide,ethyl(perfluorovinyl)disulfide, ethyl[(2-fluorophenyl)ethyl]disulfide,ethyl[(3-fluorophenyl)methyl]disulfide,ethyl[(4-fluorophenyl)methyl]disulfide,ethyl[(perfluorophenyl)methyl]disulfide,phenyl(fluoromethyl)disulfide, phenyl(difluoromethyl)disulfide,phenyl(trifluoromethyl)disulfide, phenyl(1-fluoroethyl)disulfide,phenyl(2-fluoroethyl)disulfide, phenyl(2,2,2-trifluoroethyl)disulfide,phenyl(perfluoroethyl)disulfide,phenyl(3,3,3-trifluoro-n-propyl)disulfide,phenyl(2,2,3,3,3-pentafluoro-n-propyl)disulfide,phenyl(perfluoro-n-propyl)disulfide, phenyl(2-fluoroisopropyl)disulfide,phenyl(2,2,2,2′,2′,2′-hexafluoroisopropyl)disulfide,phenyl(perfluoro-n-butyl)disulfide,phenyl(2-fluoro-tert-butyl)disulfide,phenyl(perfluoro-tert-butyl)disulfide,phenyl(2-fluorocyclohexyl)disulfide, phenyl(3-fluorocylohexyl)disulfide,phenyl(4-fluorocyclohexyl)disulfide,phenyl(perfluorocyclohexyl)disulfide, phenyl(2-fluorophenyl)disulfide,phenyl(3-fluorophenyl)disulfide, phenyl(4-fluorophenyl)disulfide,phenyl(2,3-difluorophenyl)disulfide,phenyl(2,4-difluorophenyl)disulfide,phenyl(3,5-difluorophenyl)disulfide,phenyl(2,4,6-trifluorophenyl)disulfide,phenyl(perfluorophenyl)disulfide, phenyl(1-fluorovinyl)disulfide,phenyl(2-fluorovinyl)disulfide, phenyl perfluorovinyl disulfide,phenyl[(2-fluorophenyl)methyl]disulfide,phenyl[(3-fluorophenyl)methyl]disulfide,phenyl[(4-fluorophenyl)methyl]disulfide,phenyl[(perfluorophenyl)methyl]disulfide,(2,2,2-trifluoroethyl) (2-fluorophenyl)disulfide, (2,2,2-trifluoroethyl)(3-fluorophenyl)disulfide, (2,2,2-trifluoroethyl)(4-fluorophenyl)disulfide, (2,2,2-trifluoroethyl)(2,3-difluorophenyl)disulfide, (2,2,2-trifluoroethyl)(2,4-difluorophenyl)disulfide, (2,2,2-trifluoroethyl)(3,5-difluorophenyl)disulfide, (2,2,2-trifluoroethyl)(2,4,6-trifluorophenyl)disulfide, (2,2,2-trifluoroethyl)(perfluorophenyl)disulfide, (2,2,2-trifluoroethyl)(1-fluorovinyl)disulfide, (2,2,2-trifluoroethyl)(2-fluorovinyl)disulfide, (2,2,2-trifluoroethyl)(perfluorovinyl)disulfide, (2,2,2-trifluoroethyl)[(2-fluorophenyl)methyl]disulfide, (2,2,2-trifluoroethyl)[(3-fluorophenyl)methyl]disulfide, (2,2,2-trifluoroethyl)[(4-fluorophenyl)methyl]disulfide, and (2,2,2-trifluoroethyl)[(perfluorophenyl)methyl]disulfide and the like.<1-2-8. Acid Anhydrides>

The acid anhydrides are not limited in the kind thereof. The acidanhydrides may be compounds each having two or more acid anhydridestructures per molecule. Examples of the acid anhydrides usable ininvention 3 include the anhydrides of carboxylic acids, the anhydridesof sulfonic acids, and the anhydrides of carboxylic acids and sulfonicacids.

Examples of the carboxylic acid anhydrides include

acetic anhydride, propionic anhydride, butyric anhydride, crotonicanhydride, trifluoroacetic anhydride, pentafluoropropionic anhydride,succinic anhydride, glutaric anhydride, maleic anhydride, citraconicanhydride, glutaconic anhydride, itaconic anhydride, diglycolicanhydride, cyclohexanedicarboxylic anhydride,cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2-dicarboxylicanhydride, 3,4,5,6-tetrahydrophthalic anhydride,5-norbornene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride,2-phenylglutaric anhydride, phthalic anhydride, pyromellitic anhydride,fluorosuccinic anhydride, and tetrafluorosuccinic anhydride, and thelike.

Preferred of these are

succinic anhydride, glutaric anhydride, maleic anhydride, citraconicanhydride, itaconic anhydride, diglycolic anhydride,cyclohexanedicarboxylic anhydride, fluorosuccinic anhydride, andtetrafluorosuccinic anhydride.

Examples of the sulfonic acid anhydrides include

methanesulfonic anhydride, ethanesulfonic anhydride, propanesulfonicanhydride, butanesulfonic anhydride, pentanesulfonic anhydride,hexanesulfonic anhydride, vinylsulfonic anhydride, benzenesulfonicanhydride, trifluoromethanesulfonic anhydride,2,2,2-trifluoroethanesulfonic anhydride, pentafluoroethanesulfonicanhydride, 1,2-ethanedisulfonic anhydride, 1,3-propanedisulfonicanhydride, 1,4-butanedisulfonic anhydride, 1,2-benzenedisulfonicanhydride, tetrafluoro-1,2-ethanedisulfonic anhydride,hexafluoro-1,3-propanedisulfonic anhydride,octafluoro-1,4-butanedisulfonic anhydride,3-fluoro-1,2-benzenedisulfonic anhydride, 4-fluoro-1,2-benzenedisulfonicanhydride, and 3,4,5,6-tetrafluoro-1,2-benzenedisulfonic anhydride, andthe like.

Preferred of these are

methanesulfonic anhydride, ethanesulfonic anhydride, propanesulfonicanhydride, butanesulfonic anhydride, vinylsulfonic anhydride,benzenesulfonic anhydride, trifluoromethanesulfonic anhydride,2,2,2-trifluoroethanesulfonic anhydride, pentafluoroethanesulfonicanhydride, 1,2-ethanedisulfonic anhydride, 1,3-propanedisulfonicanhydride, 1,2-benzenedisulfonic anhydride, and the like.

Examples of the anhydrides of carboxylic acids and sulfonic acidsinclude

acetic methanesulfonic anhydride, acetic ethanesulfonic anhydride,acetic propanesulfonic anhydride, propionic methanesulfonic anhydride,propionic ethanesulfonic anhydride, propionic propanesulfonic anhydride,trifluoroacetic methanesulfonic anhydride, trifluoroaceticethanesulfonic anhydride, trifluoroacetic propanesulfonic anhydride,acetic trifluoromethanesulfonic anhydride, acetic2,2,2-trifluoroethanesulfonic anhydride, aceticpentafluoroethanesulfonic anhydride, trifluoroacetictrifluoromethanesulfonic anhydride, trifluoroacetic2,2,2-trifluoroethanesulfonic anhydride, trifluoroaceticpentafluoroethanesulfonic anhydride, 3-sulfopropionic anhydride,2-methyl-3-sulfopropionic anhydride, 2,2-dimethyl-3-sulfopropionicanhydride, 2-ethyl-3-sulfopropionic anhydride,2,2-diethyl-3-sulfopropionic anhydride, 2-fluoro-3-sulfopropionicanhydride, 2,2-difluoro-3-sulfopropionic anhydride,2,2,3,3,-tetrafluoro-3-sulfopropionic anhydride, 2-sulfobenzoicanhydride, 3-fluoro-2-sulfobenzoic anhydride, 4-fluoro-2-sulfobenzoicanhydride, 5-fluoro-2-sulfobenzoic anhydride, 6-fluoro-2-sulfobenzoicanhydride, 3,6-difluoro-2-sulfobenzoic anhydride,3,4,5,6-tetrafluoro-2-sulfobenzoic anhydride,3-trifluoromethyl-2-sulfobenzoic anhydride,4-trifluoromethyl-2-sulfobenzoic anhydride,5-trifluoromethyl-2-sulfobenzoic anhydride, and6-trifluoromethyl-2-sulfobenzoic anhydride, and the like.

Preferred of these are

acetic methanesulfonic anhydride, acetic ethanesulfonic anhydride,acetic propanesulfonic anhydride, propionic methanesulfonic anhydride,propionic ethanesulfonic anhydride, propionic propanesulfonic anhydride,trifluoroacetic methanesulfonic anhydride, trifluoroaceticethanesulfonic anhydride, trifluoroacetic propanesulfonic anhydride,acetic trifluoromethanesulfonic anhydride, acetic2,2,2-trifluoroethanesulfonic anhydride, aceticpentafluoroethanesulfonic anhydride, trifluoroacetictrifluoromethanesulfonic anhydride, trifluoroacetic2,2,2-trifluoroethanesulfonic anhydride, trifluoroaceticpentafluoroethanesulfonic anhydride, 2-sulfobenzoic anhydride,3-fluoro-2-sulfobenzoic anhydride, 4-fluoro-2-sulfobenzoic anhydride,5-fluoro-2-sulfobenzoic anhydride, 6-fluoro-2-sulfobenzoic anhydride,and the like.<1-2-9. Lactone Compounds Having Substituent in α-Position>

The lactone compounds having a substituent in the α-position are notparticularly limited. Examples thereof include

β-propiolactone derivatives such as α-methyl-β-propiolactone,α-ethyl-β-propiolactone, α-propyl-β-propiolactone,α-vinyl-β-propiolactone, α-allyl-β-propiolactone,α-phenyl-β-propiolactone, α-tolyl-β-propiolactone,α-naphthyl-β-propiolactone, α-fluoro-β-propiolactone,α,α-dimethyl-β-propiolactone, α,α-diethyl-β-propiolactone,α-ethyl-α-methyl-β-propiolactone, α-methyl-α-phenyl-β-propiolactone,α,α-diphenyl-β-propiolactone, α,α-ditolyl-β-propiolactone,α,α-bis(dimethylphenyl)-β-propiolactone, α,α-dinaphthyl-β-propiolactone,α,α-divinyl-β-propiolactone, α,α-diallyl-β-propiolactone,α,α-dibenzyl-β-propiolactone, α,α-diphenethyl-β-propiolactone, andα,α-difluoro-β-propiolactone, and the like;β-butyrolactone derivatives such as α-methyl-β-butyrolactone,α-ethyl-β-butyrolactone, α-propyl-β-butyrolactone,α-vinyl-β-butyrolactone, α-allyl-β-butyrolactone,α-phenyl-β-butyrolactone, α-tolyl-β-butyrolactone,α-naphthyl-β-butyrolactone, α-fluoro-β-butyrolactone,α,α-dimethyl-β-butyrolactone, α,α-diethyl-β-butyrolactone,α-ethyl-α-methyl-β-butyrolactone, α-methyl-α-phenyl-β-butyrolactone,α,α-diphenyl-β-butyrolactone, α,α-ditolyl-β-butyrolactone,α,α-bis(dimethylphenyl)-β-butyrolactone, α,α-dinaphthyl-β-butyrolactone,α,α-divinyl-β-butyrolactone, α,α-diallyl-β-butyrolactone,α,α-dibenzyl-β-butyrolactone, α,α-diphenethyl-β-butyrolactone, andα,α-difluoro-β-butyrolactone, and the like;γ-butyrolactone derivatives such as α-methyl-γ-butyrolactone,α-ethyl-γ-butyrolactone, α-propyl-γ-butyrolactone,α-vinyl-γ-butyrolactone, α-allyl-γ-butyrolactone,α-phenyl-γ-butyrolactone, α-tolyl-γ-butyrolactone,α-naphthyl-γ-butyrolactone, α-fluoro-γ-butyrolactone,α,α-dimethyl-γ-butyrolactone, α,α-diethyl-γ-butyrolactone,α-ethyl-α-methyl-γ-butyrolactone, α-methyl-α-phenyl-γ-butyrolactone,α,α-diphenyl-γ-butyrolactone, α,α-ditolyl-γ-butyrolactone,α,α-bis(dimethylphenyl)-γ-butyrolactone, α,α-dinaphthyl-γ-butyrolactone,α,α-divinyl-γ-butyrolactone, α,α-diallyl-γ-butyrolactone,α,α-dibenzyl-γ-butyrolactone, α,α-diphenethyl-γ-butyrolactone, andα,α-difluoro-γ-butyrolactone, and the like;γ-valerolactone derivatives such as α-methyl-γ-valerolactone,α-ethyl-γ-valerolactone, α-propyl-γ-valerolactone,α-vinyl-γ-valerolactone, α-allyl-γ-valerolactone,α-phenyl-γ-valerolactone, α-tolyl-γ-valerolactone,α-naphthyl-γ-valerolactone, α-fluoro-γ-valerolactone,α,α-dimethyl-γ-valerolactone, α,α-diethyl-γ-valerolactone,α-ethyl-α-methyl-γ-valerolactone, α-methyl-α-phenyl-γ-valerolactone,α,α-diphenyl-γ-valerolactone, α,α-ditolyl-γ-valerolactone,α,α-bis(dimethylphenyl)-γ-valerolactone, α,α-dinaphthyl-γ-valerolactone,α,α-divinyl-γ-valerolactone, α,α-diallyl-γ-valerolactone,α,α-dibenzyl-γ-valerolactone, α,α-diphenethyl-γ-valerolactone, andα,α-difluoro-γ-valerolactone, and the like;δ-valerolactone derivatives such as α-methyl-δ-valerolactone,α-ethyl-δ-valerolactone, α-propyl-δ-valerolactone,α-vinyl-δ-valerolactone, α-allyl-δ-valerolactone,α-phenyl-δ-valerolactone, α-tolyl-δ-valerolactone,α-naphthyl-δ-valerolactone, α-fluoro-δ-valerolactone,α,α-dimethyl-δ-valerolactone, α,α-diethyl-δ-valerolactone,α-ethyl-α-methyl-δ-valerolactone, α-methyl-α-phenyl-δ-valerolactone,α,α-diphenyl-δ-valerolactone, α,α-ditolyl-δ-valerolactone,α,α-bis(dimethylphenyl)-δ-valerolactone, α,α-dinaphthyl-δ-valerolactone,α,α-divinyl-δ-valerolactone, α,α-diallyl-δ-valerolactone,α,α-dibenzyl-δ-valerolactone, α,α-diphenethyl-δ-valerolactone, andα,α-difluoro-δ-valerolactone;γ-caprolactone derivatives such as α-methyl-γ-caprolactone,α-ethyl-γ-caprolactone, α-propyl-γ-caprolactone, α-vinyl-γ-caprolactone,α-allyl-γ-caprolactone, α-phenyl-γ-caprolactone, α-tolyl-γ-caprolactone,α-naphthyl-γ-caprolactone, α-fluoro-γ-caprolactone,α,α-dimethyl-γ-caprolactone, α,α-diethyl-γ-caprolactone,α-ethyl-α-methyl-γ-caprolactone, α-methyl-α-phenyl-γ-caprolactone,α,α-diphenyl-γ-caprolactone, α,α-ditolyl-γ-caprolactone,α,α-bis(dimethylphenyl)-γ-caprolactone, α,α-dinaphthyl-γ-caprolactone,α,α-divinyl-γ-caprolactone, α,α-diallyl-γ-caprolactone,α,α-dibenzyl-γ-caprolactone, α,α-diphenethyl-γ-caprolactone, andα,α-difluoro-γ-caprolactone, and the like;δ-caprolactone derivatives such as α-methyl-δ-caprolactone,α-ethyl-δ-caprolactone, α-propyl-δ-caprolactone, α-vinyl-δ-caprolactone,α-allyl-δ-caprolactone, α-phenyl-δ-caprolactone, α-tolyl-δ-caprolactone,α-naphthyl-δ-caprolactone, α-fluoro-δ-caprolactone,α,α-dimethyl-δ-caprolactone, α,α-diethyl-δ-caprolactone,α-ethyl-α-methyl-δ-caprolactone, α-methyl-α-phenyl-δ-caprolactone,α,α-diphenyl-δ-caprolactone, α,α-ditolyl-δ-caprolactone,α,α-bis(dimethylphenyl)-δ-caprolactone, α,α-dinaphthyl-δ-caprolactone,α,α-divinyl-δ-caprolactone, α,α-diallyl-δ-caprolactone,α,α-dibenzyl-δ-caprolactone, α,α-diphenethyl-δ-caprolactone, andα,α-difluoro-δ-caprolactone, and the like; andε-caprolactone derivatives such as α-methyl-ε-caprolactone,α-ethyl-ε-caprolactone, α-propyl-ε-caprolactone, α-vinyl-ε-caprolactone,α-allyl-ε-caprolactone, α-phenyl-ε-caprolactone, α-tolyl-ε-caprolactone,α-naphthyl-ε-caprolactone, α-fluoro-ε-caprolactone,α,α-dimethyl-ε-caprolactone, α,α-diethyl-ε-caprolactone,α-ethyl-α-methyl-ε-caprolactone, α-methyl-α-phenyl-ε-caprolactone,α,α-diphenyl-ε-caprolactone, α,α-ditolyl-ε-caprolactone,α,α-bis(dimethylphenyl)-ε-caprolactone, α,α-dinaphthyl-ε-caprolactone,α,α-divinyl-ε-caprolactone, α,α-diallyl-ε-caprolactone,α,α-dibenzyl-ε-caprolactone, α,α-diphenethyl-ε-caprolactone, andα,α-difluoro-ε-caprolactone, and the like.

Preferred of these are

α-methyl-substituted lactones such as α-methyl-γ-butyrolactone,α-methyl-γ-valerolactone, α-methyl-δ-valerolactone, andα-methyl-δ-caprolactone etc.;

α-phenyl-substituted lactones such as α-phenyl-γ-butyrolactone,α-phenyl-γ-valerolactone, α-phenyl-δ-valerolactone, andα-phenyl-δ-caprolactone;

α,α-dimethyl-substituted lactones such as α,α-dimethyl-γ-butyrolactone,α,α-dimethyl-γ-valerolactone, α,α-dimethyl-δ-valerolactone,α,α-dimethyl-γ-caprolactone, and α,α-dimethyl-δ-caprolactone etc.; and

α,α-diphenyl-substituted lactones such as α,α-diphenyl-γ-butyrolactone,α,α-diphenyl-γ-valerolactone, α,α-diphenyl-δ-valerolactone,α,α-diphenyl-γ-caprolactone, and α,α-diphenyl-δ-caprolactone; and thelike.

More preferred of these are

α-methyl-γ-butyrolactone, α-phenyl-γ-butyrolactone,α,α-dimethyl-γ-butyrolactone, α,α-diphenyl-γ-butyrolactone, and thelike.

<1-2-10. Compounds Having Carbon-Carbon Triple Bond>

The compounds having a carbon-carbon triple bond are not particularlylimited in the kind thereof so long as they are compounds having acarbon-carbon triple bond in the molecule.

Examples of the compounds having a carbon-carbon triple bond include

carbonate compounds such as 2-propynyl methyl carbonate, 2-propynylethyl carbonate, 2-propynyl propyl carbonate, 2-propynyl butylcarbonate, 2-propynyl cyclohexyl carbonate, 2-propynyl phenyl carbonate,bis-2-propynyl carbonate, 2-butynyl methyl carbonate, 2-butynyl ethylcarbonate, 2-butynyl propyl carbonate, 2-butynyl butyl carbonate,2-butynyl cyclohexyl carbonate, 2-butynyl phenyl carbonate,bis-2-butynyl carbonate, 3-butynyl methyl carbonate, 3-butynyl ethylcarbonate, 2-pentynyl methyl carbonate, 1-methyl-2-butynyl methylcarbonate, 2-butyne-1,4-diol dimethyl carbonate, 2-butyne-1,4-dioldiethyl carbonate, 2-butyne-1,4-diol dipropyl carbonate,2-butyne-1,4-diol dicyclohexyl carbonate, and 2-butyne-1,4-diol diphenylcarbonate, and the like;carboxylic acid ester compounds such as 2-propynyl acetate, 2-propynylpropionate, 2-propynyl butyrate, 2-propynyl cyclohexanecarboxylate,2-propynyl benzoate, 2-butynyl acetate, 2-butynyl propionate, 2-butynylbutyrate, 2-butynyl cyclohexanecarboxylate, 2-butynyl benzoate,3-butynyl acetate, 3-butynyl propionate, 3-butynyl butyrate, 3-butynylcyclohexanecarboxylate, 3-butynyl benzoate, 2-pentynyl acetate,1-methyl-2-butynyl acetate, 2-butyne-1,4-diol diacetate,2-butyne-1,4-diol dipropionate, 2-butyne-1,4-dioldicyclohexanecarboxylate, and 2-butyne-1,4-diol dibenzoate etc.; andsulfonic acid ester compounds such as 2-propynyl methanesulfonate,2-propynyl ethanesulfonate, 2-propynyl propanesulfonate, 2-propynylcyclohexanesulfonate, 2-propynyl benzenesulfonate, 2-butynylmethanesulfonate, 2-butynyl ethanesulfonate, 2-butynyl propanesulfonate,2-butynyl cyclohexanesulfonate, 2-butynyl benzenesulfonate, 3-butynylmethanesulfonate, 3-butynyl ethanesulfonate, 3-butynyl propanesulfonate,3-butynyl cyclohexanesulfonate, 3-butynyl benzenesulfonate, 2-pentynylmethanesulfonate, 1-methyl-2-butynyl methanesulfonate, 2-propynyltrifluoromethanesulfonate, 2-propynyl pentafluoroethanesulfonate,2-butyne-1,4-diol dimethanesulfonate, 2-butyne-1,4-dioldipropanesulfonate, 2-butyne-1,4-diol dicyclohexanesulfonate, and2-butyne-1,4-diol dibenzenesulfonate etc.<1-2-11. Content, Technical Range, etc.>

One of such compounds enumerated above as “compound A of invention 3”,i.e., at least one compound selected from the group consisting ofcompounds represented by general formula (1), nitrile compounds,isocyanate compounds, phosphazene compounds, disulfonic acid estercompounds, sulfide compounds, disulfide compounds, acid anhydrides,lactone compounds having a substituent in the α-position, and compoundshaving a carbon-carbon triple bond, may be used alone. Alternatively,any desired combination of two or more of these compounds in any desiredproportion may be used. Furthermore, with respect to each of thoseclasses of “compound A of invention 3”, one of the compounds fallingunder the class may be used alone or any desired combination of two ormore thereof in any desired proportion may be used.

The content of the “compound A of invention 3” in nonaqueous electrolyte3 is not particularly limited. However, the total content thereof isgenerally 0.001% by mass or higher, more preferably 0.01% by mass orhigher, even more preferably 0.1% by mass or higher, based on the wholenonaqueous electrolyte. The upper limit of the total content thereof is50% by mass or lower, more preferably 25% by mass or lower, even morepreferably 10% by mass or lower, especially preferably 5% by mass orlower. When the concentration of “compound A of invention 3” is too low,there are cases where the effect of improving continuous-chargecharacteristics is difficult to obtain. On the other hand, too highconcentrations thereof may result in a decrease in charge/dischargeefficiency.

<1-3. Nonaqueous Solvent>

The nonaqueous solvent contained in nonaqueous electrolyte 3 of theinvention is not particularly limited in the use and kind thereof so logas the solvent is a nonaqueous solvent which does not adverselyinfluence battery characteristics after battery fabrication. Examplesthereof include the organic solvents enumerated above. However, it ispreferred to employ one or more of the following nonaqueous solvents foruse in nonaqueous electrolytes.

Examples of the usable nonaqueous solvents include

acyclic or cyclic carbonates, acyclic or cyclic carboxylic acid esters,acyclic or cyclic ethers, and sulfur-containing organic solvents, andthe like.

The acyclic carbonates also are not limited in the kind thereof.However, dialkyl carbonates are preferred. The number of carbon atoms ofeach constituent alkyl group is preferably 1-5, especially preferably1-4. Examples thereof include

dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyln-propyl carbonate, ethyl n-propyl carbonate, and di-n-propyl carbonate,and the like.

Of these, dimethyl carbonate, ethyl methyl carbonate, or diethylcarbonate is preferred from the standpoint of industrial availabilityand because these compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The cyclic carbonates are not limited in the kind thereof. However, thenumber of carbon atoms of the alkylene group constituting each cycliccarbonate is preferably 2-6, especially preferably 2-4. Examples of thecyclic carbonates include ethylene carbonate, propylene carbonate, andbutylene carbonate (2-ethylethylene carbonate or cis- andtrans-2,3-dimethylethylene carbonates), and the like.

Of these, ethylene carbonate or propylene carbonate is preferred becausethese compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The acyclic carboxylic acid esters also are not limited in the kindthereof. Examples thereof include

methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate,n-butyl acetate, isobutyl acetate, tert-butyl acetate, methylpropionate, ethyl propionate, n-propyl propionate, isopropyl propionate,n-butyl propionate, isobutyl propionate, and tert-butyl propionate, andthe like.

Of these, ethyl acetate, methyl propionate, or ethyl propionate ispreferred from the standpoint of industrial availability and becausethese compounds are satisfactory in various properties in anonaqueous-electrolyte secondary battery.

The cyclic carboxylic acid esters also are not limited in the kindthereof. Examples of such esters in ordinary use includeγ-butyrolactone, γ-valerolactone, and δ-valerolactone, and the like.

Of these, γ-butyrolactone is preferred from the standpoint of industrialavailability and because this compound is satisfactory in variousproperties in a nonaqueous-electrolyte secondary battery.

The acyclic ethers also are not limited in the kind thereof. Examplesthereof include

dimethoxymethane, dimethoxyethane, diethoxymethane, diethoxyethane,ethoxymethoxymethane, and ethoxymethoxyethane, and the like.

Of these, dimethoxyethane or diethoxyethane is preferred from thestandpoint of industrial availability and because these compounds aresatisfactory in various properties in a nonaqueous-electrolyte secondarybattery.

The cyclic ethers also are not limited in the kind thereof. Examplesthereof include

tetrahydrofuran, 2-methyltetrahydrofuran, and tetrahydropyran, and thelike.

Furthermore, the sulfur-containing organic solvents also are notparticularly limited in the kind thereof. Examples thereof include

ethylene sulfite, 1,3-propanesultone, 1,4-butanesultone, methylmethanesulfonate, sulfolane, and sulfolene and the like.

Of those compounds, the acyclic or cyclic carbonates or the acyclic orcyclic carboxylic acid esters are preferred because these compounds aresatisfactory in various properties in a nonaqueous-electrolyte secondarybattery. More preferred of these is ethylene carbonate, propylenecarbonate, dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, ethyl acetate, methyl propionate, ethyl propionate, orγ-butyrolactone. Even more preferred is ethylene carbonate, propylenecarbonate, dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, ethyl acetate, methyl propionate, or γ-butyrolactone.

Those compounds may be used alone or in combination of two or morethereof. It is, however, preferred to use two or more compounds incombination. For example, it is especially preferred to use ahigh-permittivity solvent, such as a cyclic carbonate, in combinationwith a low-viscosity solvent, such as an acyclic carbonate or an acyclicester.

A preferred combination of nonaqueous solvents is a combinationconsisting mainly of at least one cyclic carbonate and at least oneacyclic carbonate. In particular, the total proportion of the cycliccarbonate and the acyclic carbonate to the whole nonaqueous solvent isgenerally 80% by volume or higher, preferably 85% by volume or higher,more preferably 90% by volume or higher. The proportion by volume of thecyclic carbonate to the sum of the cyclic carbonate and the acycliccarbonate is preferably 5% by volume or higher, more preferably 10% byvolume or higher, especially preferably 15% by volume or higher, and isgenerally 50% by volume or lower, preferably 35% by volume or lower,more preferably 30% or lower. Use of such combination of nonaqueoussolvents is preferred because the battery fabricated with thiscombination has an improved balance between cycle characteristics andhigh-temperature storability (in particular, residual capacity andhigh-load discharge capacity after high-temperature storage).

Examples of the preferred combination including at least one cycliccarbonate and at least one acyclic carbonate include: ethylene carbonateand dimethyl carbonate; ethylene carbonate and diethyl carbonate;ethylene carbonate and ethyl methyl carbonate; ethylene carbonate,dimethyl carbonate, and diethyl carbonate; ethylene carbonate, dimethylcarbonate, and ethyl methyl carbonate; ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate; and ethylene carbonate, dimethylcarbonate, diethyl carbonate, and ethyl methyl carbonate, and the like.

Combinations obtained by further adding propylene carbonate to thosecombinations including ethylene carbonate and one or more acycliccarbonates are also included in preferred combinations. In the casewhere propylene carbonate is contained, the volume ratio of the ethylenecarbonate to the propylene carbonate is preferably from 99:1 to 40:60,especially preferably from 95:5 to 50:50. It is also preferred toregulate the proportion of the propylene carbonate to the wholenonaqueous solvent to a value which is 0.1% by volume or higher,preferably 1% by volume or higher, more preferably 2% by volume orhigher, and is generally 10% by volume or lower, preferably 8% by volumeor lower, more preferably 5% by volume or lower. This is because thisregulation brings about excellent discharge load characteristics whilemaintaining the properties of the combination of ethylene carbonate andone or more acyclic carbonates.

More preferred of these are combinations including an asymmetric acycliccarbonate. In particular, combinations including ethylene carbonate, asymmetric acyclic carbonate, and an asymmetric acyclic carbonate, suchas a combination of ethylene carbonate, dimethyl carbonate, and ethylmethyl carbonate, a combination of ethylene carbonate, diethylcarbonate, and ethyl methyl carbonate, and a combination of ethylenecarbonate, dimethyl carbonate, diethyl carbonate, and ethyl methylcarbonate, or such combinations which further contain propylenecarbonate are preferred because these combinations have a satisfactorybalance between cycle characteristics and discharge loadcharacteristics. Preferred of such combinations are ones in which theasymmetric acyclic carbonate is ethyl methyl carbonate. Furthermore, thenumber of carbon atoms of each of the alkyl groups constituting eachdialkyl carbonate is preferably 1-2.

Other examples of preferred mixed solvents are ones containing anacyclic ester. In particular, the cyclic carbonate/acyclic carbonatemixed solvents which contain an acyclic ester are preferred from thestandpoint of improving the discharge load characteristics of a battery.The acyclic ester especially preferably is methyl acetate, ethylacetate, or methyl propionate. The proportion by volume of the acyclicester to the whole nonaqueous solvent is generally 50 or higher,preferably 8% or higher, more preferably 15% or higher, and is generally50% or lower, preferably 35% or lower, more preferably 30% or lower,even more preferably 25% or lower.

Other preferred examples of the nonaqueous solvent are ones in which oneorganic solvent selected from the group consisting of ethylenecarbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, andγ-valerolactone or a mixed solvent composed of two or more organicsolvents selected from the group accounts for at least 60% by volume ofthe whole. Such mixed solvents have a flash point of preferably 50° C.or higher, especially preferably 70° C. or higher. Nonaqueouselectrolyte 3 employing this solvent is reduced in solvent vaporizationand liquid leakage even when used at high temperatures. In particular,when such a nonaqueous solvent which includes ethylene carbonate andγ-butyrolactone in a total amount of 80% by volume or larger, preferably90% by volume or larger, based on the whole nonaqueous solvent and inwhich the volume ratio of the ethylene carbonate to the γ-butyrolactoneis from 5:95 to 45:55 or such a nonaqueous solvent which includesethylene carbonate and propylene carbonate in a total amount of 80% byvolume or larger, preferably 90% by volume or larger, based on the wholenonaqueous solvent and in which the volume ratio of the ethylenecarbonate to the propylene carbonate is from 30:70 to 80:20 is used,then an improved balance between cycle characteristics and dischargeload characteristics, etc. is generally obtained.

<1-4. Monofluorophosphate and Difluorophosphate>

Nonaqueous electrolyte 3 of the invention contains a monofluorophosphateand/or a difluorophosphate as an essential component. With respect tothe “monofluorophosphate and difluorophosphate” to be used in invention3, the kinds and contents thereof, places where the salts exist, methodsof analysis, production process, etc. are the same as those describedabove with regard to nonaqueous electrolyte 1.

<1-5. Additives>

Nonaqueous electrolyte 3 of the invention may contain various additivesso long as these additives do not considerably lessen the effects ofinvention 3. In the case where additives are additionally incorporatedto prepare the nonaqueous electrolyte, conventionally known additivescan be used at will. One additive may be used alone, or any desiredcombination of two or more additives in any desired proportion may beused.

Examples of the additives include overcharge inhibitors and aids forimproving capacity retentivity and cycle characteristics afterhigh-temperature storage. It is preferred to add a carbonate having atleast either of an unsaturated bond and a halogen atom (hereinaftersometimes referred to as “specific carbonate”) as an aid for improvingcapacity retentivity after high-temperature storage and cyclecharacteristics, among those additives. The specific carbonate and otheradditives are separately explained below.

<1-5-1. Specific Carbonate>

The specific carbonate is a carbonate having at least either of anunsaturated bond and a halogen atom. The specific carbonate may have anunsaturated bond only or have a halogen atom only, or may have both anunsaturated bond and a halogen atom.

The molecular weight of the specific carbonate is not particularlylimited, and may be any desired value unless this considerably lessensthe effects of invention 3. However, the molecular weight thereof isgenerally 50 or higher, preferably 80 or higher, and is generally 250 orlower, preferably 150 or lower. When the molecular weight thereof is toohigh, this specific carbonate has reduced solubility in nonaqueouselectrolyte 3 and there are cases where the effect of the carbonate isdifficult to produce sufficiently.

Processes for producing the specific carbonate also are not particularlylimited, and a known process selected at will can be used to produce thecarbonate.

Any one specific carbonate may be incorporated alone into nonaqueouselectrolyte 3 of the invention, or any desired combination of two ormore specific carbonates may be incorporated thereinto in any desiredproportion.

The amount of the specific carbonate to be incorporated into nonaqueouselectrolyte 3 of the invention is not limited, and may be any desiredvalue unless this considerably lessens the effects of invention 3. Itis, however, desirable that the specific carbonate should beincorporated in a concentration which is generally 0.01% by mass orhigher, preferably 0.1% by mass or higher, more preferably 0.3% by massor higher, and is generally 70% by mass or lower, preferably 50% by massor lower, more preferably 40% by mass or lower, based on nonaqueouselectrolyte 3 of the invention. In particular, in the case of acarbonate having an unsaturated bond, it is preferred to incorporatethis carbonate in an amount of 10% by mass or smaller based onnonaqueous electrolyte 3.

When the amount of the specific carbonate is below the lower limit ofthat range, there are cases where use of this nonaqueous electrolyte 3of the invention in a nonaqueous-electrolyte secondary battery resultsin difficulties in producing the effect of sufficiently improving thecycle characteristics of the nonaqueous-electrolyte secondary battery.On the other hand, when the proportion of the specific carbonate is toohigh, there is a tendency that use of this nonaqueous electrolyte 3 ofthe invention in a nonaqueous-electrolyte secondary battery results indecreases in the high-temperature storability and continuous-chargecharacteristics of the nonaqueous-electrolyte secondary battery. Inparticular, there are cases where gas evolution is enhanced and capacityretentivity decreases.

<1-5-1-1. Unsaturated Carbonate>

The carbonate having an unsaturated bond (hereinafter often referred toas “unsaturated carbonate”) as one form of the specific carbonateaccording to invention 3 is not limited so long as it is a carbonatehaving a carbon-carbon double bond, and any desired unsaturatedcarbonate can be used. Incidentally, carbonates having one or morearomatic rings are also included in the carbonate having an unsaturatedbond.

Examples of the unsaturated carbonate include vinylene carbonate andderivatives thereof, ethylene carbonate derivatives substituted with oneor more aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond, phenyl carbonates, vinyl carbonates, andallyl carbonates.

Examples of the vinylene carbonate and derivatives thereof includevinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylenecarbonate, phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, andcatechol carbonate, and the like.

Examples of the ethylene carbonate derivatives substituted with one ormore aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond include vinylethylene carbonate,4,5-divinylethylene carbonate, phenylethylene carbonate, and4,5-diphenylethylene carbonate, and the like.

Examples of the phenyl carbonates include diphenyl carbonate, ethylphenyl carbonate, methyl phenyl carbonate, and t-butyl phenyl carbonate,and the like.

Examples of the vinyl carbonates include divinyl carbonate and methylvinyl carbonate, and the like.

Examples of the allyl carbonates include diallyl carbonate and allylmethyl carbonate, and the like.

Preferred of these unsaturated carbonates as examples of the specificcarbonate are the vinylene carbonate and derivatives thereof and theethylene carbonate derivatives substituted with one or more aromaticrings or with one or more substituents having a carbon-carbonunsaturated bond. In particular, vinylene carbonate,4,5-diphenylvinylene carbonate, 4,5-dimethylvinylene carbonate, orvinylethylene carbonate is more preferred because these carbonates forma stable interface-protective coating film.

<1-5-1-2. Halogenated Carbonate>

On the other hand, the carbonate having a halogen atom (hereinafteroften referred to as “halogenated carbonate”) as one form of thespecific carbonate according to invention 3 is not particularly limitedso long as it is a carbonate having a halogen atom, and any desiredhalogenated carbonate can be used.

Examples of the halogen atoms include fluorine, chlorine, bromine, andiodine atoms. Preferred of these are fluorine atoms or chlorine atoms.Especially preferred are fluorine atoms. The number of halogen atomspossessed by the halogenated carbonate also is not particularly limitedso long as the number thereof is 1 or larger. However, the numberthereof is generally 6 or smaller, preferably 4 or smaller. In the casewhere the halogenated carbonate has two or more halogen atoms, theseatoms may be the same or different.

Examples of the halogenated carbonate include ethylene carbonatederivatives, dimethyl carbonate derivatives, ethyl methyl carbonatederivatives, and diethyl carbonate derivatives.

Examples of the ethylene carbonate derivatives include

fluoroethylene carbonate, chloroethylene carbonate, 4,4-difluoroethylenecarbonate, 4,5-difluoroethylene carbonate, 4,4-dichloroethylenecarbonate, 4,5-dichloroethylene carbonate, 4-fluoro-4-methylethylenecarbonate, 4-chloro-4-methylethylene carbonate,4,5-difluoro-4-methylethylene carbonate, 4,5-dichloro-4-methylethylenecarbonate, 4-fluoro-5-methylethylene carbonate,4-chloro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylenecarbonate, 4,4-dichloro-5-methylethylene carbonate,4-(fluoromethyl)ethylene carbonate, 4-(chloromethyl)-ethylene carbonate,4-(difluoromethyl)-ethylene carbonate, 4-(dichloromethyl)-ethylenecarbonate, 4-(trifluoromethyl)-ethylene carbonate,4-(trichloromethyl)-ethylene carbonate,4-(fluoromethyl)-4-fluoroethylene carbonate,4-(chloromethyl)-4-chloroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-(chloromethyl)-5-chloroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate, 4-chloro-4,5-dimethylethylenecarbonate, 4,5-difluoro-4,5-dimethylethylene carbonate,4,5-dichloro-4,5-dimethylethylene carbonate,4,4-difluoro-5,5-dimethylethylene carbonate, and4,4-dichloro-5,5-dimethylethylene carbonate, and the like.

Examples of the dimethyl carbonate derivatives include

fluoromethyl methyl carbonate, difluoromethyl methyl carbonate,trifluoromethyl methyl carbonate, bis(fluoromethyl)carbonate,bis(difluoromethyl)carbonate, bis(trifluoromethyl)carbonate,chloromethyl methyl carbonate, dichloromethyl methyl carbonate,trichloromethyl methyl carbonate, bis(chloromethyl)carbonate,bis(dichloromethyl)carbonate, and bis(trichloromethyl)carbonate, and thelike.

Examples of the ethyl methyl carbonate derivatives include

2-fluoroethyl methyl carbonate, ethyl fluoromethyl carbonate,2,2-difluoroethyl methyl carbonate, 2-fluoroethyl fluoromethylcarbonate, ethyl difluoromethyl carbonate, 2,2,2-trifluoroethyl methylcarbonate, 2,2-difluoroethyl fluoromethyl carbonate, 2-fluoroethyldifluoromethyl carbonate, ethyl trifluoromethyl carbonate, 2-chloroethylmethyl carbonate, ethyl chloromethyl carbonate, 2,2-dichloroethyl methylcarbonate, 2-chloroethyl chloromethyl carbonate, ethyl dichloromethylcarbonate, 2,2,2-trichloroethyl methyl carbonate, 2,2-dichloroethylchloromethyl carbonate, 2-chloroethyl dichloromethyl carbonate, andethyl trichloromethyl carbonate, and the like.

Examples of the diethyl carbonate derivatives includeethyl(2-fluoroethyl)carbonate, ethyl(2,2-difluoroethyl)carbonate,bis(2-fluoroethyl)carbonate, ethyl(2,2,2-trifluoroethyl)carbonate,2,2-difluoroethyl 2′-fluoroethyl carbonate,bis(2,2-difluoroethyl)carbonate, 2,2,2-trifluoroethyl-2′-fluoroethylcarbonate, 2,2,2-trifluoroethyl-2′,2′-difluoroethyl carbonate,bis(2,2,2-trifluoroethyl)carbonate, ethyl-(2-chloroethyl)carbonate,ethyl-(2,2-dichloroethyl)carbonate, bis(2-chloroethyl)carbonate,ethyl-(2,2,2-trichloroethyl)carbonate, 2,2-dichloroethyl-2′-chloroethylcarbonate, bis(2,2-dichloroethyl)carbonate,2,2,2-trichloroethyl-2′-chloroethyl carbonate, 2,2,2-trichloroethyl2′,2′-dichloroethyl carbonate, and bis(2,2,2-trichloroethyl)carbonate,and the like.

Preferred of these halogenated carbonates are the carbonates having afluorine atom. More preferred are the carbonate derivatives having afluorine atom. In particular, fluoroethylene carbonate,4-(fluoromethyl)-ethylene carbonate, 4,4-difluoroethylene carbonate, and4,5-difluoroethylene carbonate are more suitable because thesecarbonates form an interface-protective coating film.

<1-5-1-3. Halogenated Unsaturated Carbonate>

Furthermore usable as the specific carbonate is a carbonate having bothan unsaturated bond and a halogen atom (referred to as “halogenatedunsaturated carbonate”). This halogenated unsaturated carbonate is notparticularly limited, and any desired halogenated unsaturated carbonatecan be used unless the effects of invention 3 are considerably lessenedthereby.

Examples of the halogenated unsaturated carbonate include vinylenecarbonate derivatives, ethylene carbonate derivatives substituted withone or more aromatic rings or with one or more substituents having acarbon-carbon unsaturated bond, and allyl carbonates. With respect tothe “halogenated unsaturated carbonate” in nonaqueous electrolyte 3, thesame explanation as that given above with regard to nonaqueouselectrolyte 2 applies.

<1-5-2. Other Additives>

Additives other than the specific carbonate are explained below.Examples of additives other than the specific carbonate includeovercharge inhibitors and aids for improving capacity retentivity afterhigh-temperature storage and cycle characteristics.

<1-5-2-1. Overcharge Inhibitor>

Examples of the overcharge inhibitor, content thereof, examples ofcombinations in the case of using compounds in different classes incombination, effects of the incorporation thereof, etc. are the same asthose described above with regard to nonaqueous electrolyte 1.

<1-4-2. Other Additives>

Examples of additives other than the specific carbonate includeovercharge inhibitors and aids for improving capacity retentivity afterhigh-temperature storage and cycle characteristics. The “overchargeinhibitors” and the “aids for improving capacity retentivity afterhigh-temperature storage and cycle characteristics” are the same asthose described above with regard to nonaqueous electrolyte 1. It is,however, noted that the “compound A of invention 3” is excluded from theother additives.

<1-5-2-2. Aids>

Examples of the aids for improving capacity retentivity afterhigh-temperature storage include and cycle characteristics carbonatecompounds other than the specific carbonates, such as erythritancarbonate and spiro-bis-dimethylene carbonate etc.; sulfur-containingcompounds such as ethylene sulfite, 1,3-propanesultone,1,4-butanesultone, methyl methanesulfonate, sulfolane, sulfolene,dimethyl sulfone, diphenyl sulfone, methyl phenyl sulfone,tetramethylthiuram monosulfide, N,N-dimethylmethanesulfonamide, andN,N-diethylmethanesulfonamide etc.;

nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone,1-methyl-2-piperidone, 3-methyl-2-oxazolidinone,1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide etc.; and

hydrocarbon compounds such as heptane, octane, and cycloheptane etc.

[2. Nonaqueous-Electrolyte Secondary Battery]

Nonaqueous-electrolyte secondary battery 3 of the invention includes: anegative electrode and a positive electrode which are capable ofoccluding and releasing ions; and the nonaqueous electrolyte 3 of theinvention.

<2-1. Battery Constitution>

Nonaqueous-electrolyte secondary battery 3 of the invention may have thesame battery constitution as that described above with regard tononaqueous-electrolyte secondary battery 1.

<2-2. Nonaqueous Electrolyte>

As the nonaqueous electrolyte, the nonaqueous electrolyte 3 of theinvention described above is used. Incidentally, a mixture of nonaqueouselectrolyte 3 of the invention and another nonaqueous electrolyte may beused so long as this is not counter to the spirit of invention 3.

<2-3. Negative Electrode>

The negative electrode of nonaqueous-electrolyte secondary battery 3 maybe the same as the negative electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-4. Positive Electrode>

The positive electrode of nonaqueous-electrolyte secondary battery 3 maybe the same as the positive electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-5. Separator>

The separator of nonaqueous-electrolyte secondary battery 3 may be thesame as the separator described above with regard tononaqueous-electrolyte secondary battery 1.

<2-6. Battery Design>

The battery design of nonaqueous-electrolyte secondary battery 3 may bethe same as the battery design described above with regard tononaqueous-electrolyte secondary battery 1.

[1. Nonaqueous Electrolyte 4]

Like ordinary nonaqueous electrolytes, nonaqueous electrolyte 4 of theinvention includes an electrolyte and a nonaqueous solvent containingthe electrolyte dissolved therein. Usually, the electrolyte and thesolvent are contained as main components.

<1-1. Electrolyte>

As the electrolyte in invention 4, one or more lithium salts aregenerally used. The lithium salts are not particularly limited so longas they are known to be usable in this application. Any desired suchlithium salts can be used. Examples thereof are the same as thoseenumerated above with regard to the electrolyte in nonaqueouselectrolyte 1. Specifically, the following are included in preferredexamples.

Preferred examples thereof include

inorganic lithium salts such as LiPF₆ and LiBF₄ etc.;

fluorine-containing organic lithium salts such as LiCF₃SO₃,LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, the lithium salt of cyclic1,2-perfluoroethanedisulfonylimide, the lithium salt of cyclic1,3-perfluoropropanedisulfonylimide, LiN(CF₃SO₂) (C₄F₉SO₂),LiC(CF₃SO₂)₃, LiPF₄ (CF₃)₂, LiPF₄ (C₂F₅)₂, LiPF₄ (CF₃SO₂)₂, LiPF₄(C₂F₅SO₂)₂, LiBF₂ (CF₃)₂, LiBF₂ (C₂F₅)₂, LiBF₂ (CF₃SO₂)₂, and LiBF₂(C₂F₅SO₂)₂ etc.; andlithium bis(oxalato)borate etc.

Preferred of these is LiPF₆, LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂, orLiN(C₂F₅SO₂)₂ from the standpoint of improving battery performances.Especially preferred is LiPF₆ or LiBF₄. These lithium salts may be usedalone or in combination of two or more thereof. One preferred example inthe case of using two or more lithium salts in combination is acombination of LiPF₆ and LiBF₄. This combination has the effect ofimproving cycle characteristics. In this case, the proportion of theLiBF₄ to the sum of the two is preferably 0.01% by mass or higher,especially preferably 0.1% by mass or higher, and is preferably 20% bymass or lower, especially preferably 5% by mass or lower. When theproportion thereof is lower than the lower limit, there are cases wherethe desired effect is not obtained. In case where the proportion thereofexceeds the upper limit, battery characteristics after high-temperaturestorage tend to decrease.

Another example is a combination of an inorganic lithium salt and afluorine-containing organic lithium salt. In this case, the proportionof the inorganic lithium salt to the sum of the two is desirably from70% by mass to 99% by mass. The fluorine-containing organic lithium saltpreferably is any of LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, the lithium salt ofcyclic 1,2-perfluoroethanedisulfonylimide, and the lithium salt ofcyclic 1,3-perfluoropropanedisulfonylimide. Use of this combination hasthe effect of inhibiting the deterioration caused by high-temperaturestorage.

The concentration of these electrolytes in nonaqueous electrolyte 4 isnot particularly limited. However, the concentration thereof isgenerally 0.5 mol/L or higher, preferably 0.6 mol/L or higher, morepreferably 0.7 mol/L or higher. The upper limit thereof is generally 3mol/L or lower, preferably 2 mol/L or lower, more preferably 1.8 mol/Lor lower, especially preferably 1.5 mol/L or lower. When theconcentration of the electrolytes is too low, there are cases where thiselectrolyte has insufficient electrical conductivity. On the other hand,when the concentration thereof is too high, there are cases where anincrease in viscosity results and this reduces electrical conductivity.There also are cases where battery performances decrease.

Nonaqueous electrolyte 4 of the invention includes an electrolyte and anonaqueous solvent containing the electrolyte dissolved therein. Thisnonaqueous electrolyte 4 at least contains a cyclic sulfone compound, “acompound having a coefficient of viscosity at 25° C. of 1.5 mPa·s orlower”, and “at least one compound selected from the group consisting ofcarbonates having an unsaturated bond, carbonates having a halogen atom,monofluorophosphates, and difluorophosphates”.

<1-2. Cyclic Sulfone Compound>

The “cyclic sulfone compound” is not particularly limited so long as itis a cyclic compound in which the cyclic moiety is constituted of one ormore methylene groups and one or more sulfone groups. Any desired cyclicsulfone compound can be used. Preferred of such compounds are ones inwhich the cyclic moiety is constituted of three or more methylene groupsand one or more sulfone groups and which have a molecular weight of 500or lower.

Examples of the cyclic sulfone compound include: monosulfone compoundsincluding trimethylene sulfone compounds, tetramethylene sulfonecompounds, and hexamethylene sulfone compounds; and disulfone compoundsincluding trimethylene disulfone compounds, tetramethylene disulfonecompounds, and hexamethylene disulfone compounds. More preferred ofthese from the standpoints of permittivity and viscosity aretetramethylene sulfone compounds, tetramethylene disulfone compounds,hexamethylene sulfone compounds, and hexamethylene disulfone compounds.Especially preferred are tetramethylene sulfone compounds (sulfolanecompounds).

The cyclic sulfone compound preferably is sulfolane and/or a sulfolanederivative (hereinafter, the derivative and sulfolane are sometimesreferred to inclusively as “sulfolane compound”), from the standpoint ofproducing the effects of the invention. Especially preferred ofsulfolane derivatives are sulfolane derivatives in which one or more ofthe hydrogen atoms bonded to the carbon atoms constituting the sulfolanering have been replaced with halogen atoms. Furthermore, sulfolanederivatives having one or more alkyl groups to such a degree as not tolessen the effects of the invention are also preferred. Moreover, suchsulfolane derivatives in which one or more of the hydrogen atoms bondedto the carbon atoms constituting the alkyl groups have been replacedwith halogen atoms are also especially preferred.

Examples of the halogen atoms include fluorine, chlorine, bromine, andiodine atoms. Preferred of these are fluorine atoms or chlorine atoms.Especially preferred are fluorine atoms. These (especially) preferredhalogen atoms apply to both the halogen atoms bonded to the carbon atomsconstituting the sulfolane ring and the halogen atoms bonded to thealkyl group(s) bonded to the sulfolane ring.

Examples of sulfolane derivatives containing one or more alkylsubstituents include

2-methylsulfolane, 3-methylsulfolane, 2,2-dimethylsulfolane,3,3-dimethylsulfolane, 2,3-dimethylsulfolane, 2,4-dimethylsulfolane,2,5-dimethylsulfolane, 2,2,3-trimethylsulfolane,2,2,4-trimethylsulfolane, 2,2,5-trimethylsulfolane,2,3,3-trimethylsulfolane, 3,3,4-trimethylsulfolane,3,3,5-trimethylsulfolane, 2,3,4-trimethylsulfolane,2,3,5-trimethylsulfolane, 2,2,3,3-tetramethylsulfolane,2,2,3,4-tetramethylsulfolane, 2,2,3,5-tetramethylsulfolane,2,2,4,4-tetramethylsulfolane, 2,2,4,5-tetramethylsulfolane,2,2,5,5-tetramethylsulfolane, 2,3,3,4-tetramethylsulfolane,2,3,3,5-tetramethylsulfolane, 2,3,4,4-tetramethylsulfolane,2,3,4,5-tetramethylsulfolane, 3,3,4,4-tetramethylsulfolane,2,2,3,3,4-pentamethylsulfolane, 2,2,3,3,5-pentamethylsulfolane,2,2,3,4,4-pentamethylsulfolane, 2,2,3,4,5-pentamethylsulfolane,2,3,3,4,4-pentamethylsulfolane, 2,3,3,4,5-pentamethylsulfolane,2,2,3,3,4,4-hexamethylsulfolane, 2,2,3,3,4,5-hexamethylsulfolane,2,2,3,3,5,5-hexamethylsulfolane, 2,2,3,4,5,5-hexamethylsulfolane,2,2,3,3,4,4,5-heptamethylsulfolane, 2,2,3,3,4,5,5-heptamethylsulfolane,and octamethylsulfolane, and the like.

Examples of sulfolane derivatives having no substituents and containinga fluorine atom include

2-fluorosulfolane, 3-fluorosulfolane, 2,2-difluorosulfolane,2,3-difluorosulfolane, 2,4-difluorosulfolane, 2,5-difluorosulfolane,3,4-difluorosulfolane, 2,2,3-trifluorosulfolane,2,3,3-trifluorosulfolane, 2,2,4-trifluorosulfolane,2,2,5-trifluorosulfolane, 2,3,4-trifluorosulfolane,2,3,5-trifluorosulfolane, 2,4,4-trifluorosulfolane,2,2,3,3-tetrafluorosulfolane, 2,2,3,4-tetrafluorosulfolane,2,2,4,4-tetrafluorosulfolane, 2,2,5,5-tetrafluorosulfolane,2,3,3,4-tetrafluorosulfolane, 2,3,3,5-tetrafluorosulfolane,2,3,4,4-tetrafluorosulfolane, 2,3,4,5-tetrafluorosulfolane,2,2,3,3,4-pentafluorosulfolane, 2,2,3,3,5-pentafluorosulfolane,2,2,3,4,4-pentafluorosulfolane, 2,2,3,4,5-pentafluorosulfolane,2,3,3,4,4-pentafluorosulfolane, 2,3,3,4,5-pentafluorosulfolane,2,2,3,3,4,4-hexafluorosulfolane, 2,2,3,3,4,5-hexafluorosulfolane,2,2,3,3,5,5-hexafluorosulfolane, 2,2,3,4,5,5-hexafluorosulfolane,2,2,3,3,4,4,5-heptafluorosulfolane, 2,2,3,3,4,5,5-heptafluorosulfolane,and octafluorosulfolane.

Examples of sulfolane derivatives having one or more alkyl substituentsand a fluorine atom include

2-fluoro-3-methylsulfolane, 2-fluoro-2-methylsulfolane,3-fluoro-3-methylsulfolane, 3-fluoro-2-methylsulfolane,4-fluoro-3-methylsulfolane, 4-fluoro-2-methylsulfolane,5-fluoro-3-methylsulfolane, 5-fluoro-2-methylsulfolane,2-fluoro-2,4-dimethylsulfolane, 4-fluoro-2,4-dimethylsulfolane,5-fluoro-2,4-dimethylsulfolane, 2,2-difluoro-3-methylsulfolane,2,3-difluoro-3-methylsulfolane, 2,4-difluoro-3-methylsulfolane,2,5-difluoro-3-methylsulfolane, 3,4-difluoro-3-methylsulfolane,3,5-difluoro-3-methylsulfolane, 4,4-difluoro-3-methylsulfolane,4,5-difluoro-3-methylsulfolane, 5,5-difluoro-3-methylsulfolane,2,2,3-trifluoro-3-methylsulfolane, 2,2,4-trifluoro-3-methylsulfolane,2,2,5-trifluoro-3-methylsulfolane, 2,3,4-trifluoro-3-methylsulfolane,2,3,5-trifluoro-3-methylsulfolane, 2,4,4-trifluoro-3-methylsulfolane,2,4,5-trifluoro-3-methylsulfolane, 2,5,5-trifluoro-3-methylsulfolane,3,4,4-trifluoro-3-methylsulfolane, 3,4,5-trifluoro-3-methylsulfolane,4,4,5-trifluoro-3-methylsulfolane, 4,5,5-trifluoro-3-methylsulfolane,2,2,3,4-tetrafluoro-3-methylsulfolane,2,2,3,5-tetrafluoro-3-methylsulfolane,2,2,4,4-tetrafluoro-3-methylsulfolane,2,2,4,5-tetrafluoro-3-methylsulfolane,2,2,5,5-tetrafluoro-3-methylsulfolane,2,3,4,4-tetrafluoro-3-methylsulfolane,2,3,4,5-tetrafluoro-3-methylsulfolane,2,3,5,5-tetrafluoro-3-methylsulfolane,3,4,4,5-tetrafluoro-3-methylsulfolane,3,4,5,5-tetrafluoro-3-methylsulfolane,4,4,5,5-tetrafluoro-3-methylsulfolane,2,2,3,4,4-pentafluoro-3-methylsulfolane,2,2,3,4,5-pentafluoro-3-methylsulfolane,2,2,3,5,5-pentafluoro-3-methylsulfolane,2,3,4,4,5-pentafluoro-3-methylsulfolane,2,3,4,5,5-pentafluoro-3-methylsulfolane,2,2,3,4,4,5-hexafluoro-3-methylsulfolane,2,2,3,4,5,5-hexafluoro-3-methylsulfolane,2,3,4,4,5,5-hexafluoro-3-methylsulfolane, andheptafluoro-3-methylsulfolane, and the like.

Examples of sulfolane derivatives having a monofluoroalkyl substituentand a fluorine atom include

2-fluoro-3-(fluoromethyl)sulfolane, 3-fluoro-3-(fluoromethyl)sulfolane,4-fluoro-3-(fluoromethyl)sulfolane, 5-fluoro-3-(fluoromethyl)sulfolane,2,2-difluoro-3-(fluoromethyl)sulfolane,2,3-difluoro-3-(fluoromethyl)sulfolane,2,4-difluoro-3-(fluoromethyl)sulfolane,2,5-difluoro-3-(fluoromethyl)sulfolane,3,4-difluoro-3-(fluoromethyl)sulfolane,3,5-difluoro-3-(fluoromethyl)sulfolane,4,4-difluoro-3-(fluoromethyl)sulfolane,4,5-difluoro-3-(fluoromethyl)sulfolane,5,5-difluoro-3-(fluoromethyl)sulfolane,2,2,3-trifluoro-3-(fluoromethyl)sulfolane,2,2,4-trifluoro-3-(fluoromethyl)sulfolane,2,2,5-trifluoro-3-(fluoromethyl)sulfolane,2,3,4-trifluoro-3-(fluoromethyl)sulfolane,2,3,5-trifluoro-3-(fluoromethyl)sulfolane,2,4,4-trifluoro-3-(fluoromethyl)sulfolane,2,4,5-trifluoro-3-(fluoromethyl)sulfolane,2,5,5-trifluoro-3-(fluoromethyl)sulfolane,3,4,4-trifluoro-3-(fluoromethyl)sulfolane,3,4,5-trifluoro-3-(fluoromethyl)sulfolane,4,4,5-trifluoro-3-(fluoromethyl)sulfolane,4,5,5-trifluoro-3-(fluoromethyl)sulfolane,2,2,3,4-tetrafluoro-3-(fluoromethyl)sulfolane,2,2,3,5-tetrafluoro-3-(fluoromethyl)sulfolane,2,2,4,4-tetrafluoro-3-(fluoromethyl)sulfolane,2,2,4,5-tetrafluoro-3-(fluoromethyl)sulfolane,2,2,5,5-tetrafluoro-3-(fluoromethyl)sulfolane,2,3,4,4-tetrafluoro-3-(fluoromethyl)sulfolane,2,3,4,5-tetrafluoro-3-(fluoromethyl)sulfolane,2,3,5,5-tetrafluoro-3-(fluoromethyl)sulfolane,3,4,4,5-tetrafluoro-3-(fluoromethyl)sulfolane,3,4,5,5-tetrafluoro-3-(fluoromethyl)sulfolane,4,4,5,5-tetrafluoro-3-(fluoromethyl)sulfolane,2,2,3,4,4-pentafluoro-3-(fluoromethyl)sulfolane,2,2,3,4,5-pentafluoro-3-(fluoromethyl)sulfolane,2,2,3,5,5-pentafluoro-3-(fluoromethyl)sulfolane,2,3,4,4,5-pentafluoro-3-(fluoromethyl)sulfolane,2,3,4,5,5-pentafluoro-3-(fluoromethyl)sulfolane,2,2,3,4,4,5-hexafluoro-3-(fluoromethyl)sulfolane,2,2,3,4,5,5-hexafluoro-3-(fluoromethyl)sulfolane,2,3,4,4,5,5-hexafluoro-3-(fluoromethyl)sulfolane, andheptafluoro-3-(fluoromethyl)sulfolane, and the like.

Examples of sulfolane derivatives having a difluoroalkyl substituent anda fluorine atom include

2-fluoro-3-(difluoromethyl)sulfolane,3-fluoro-3-(difluoromethyl)sulfolane,4-fluoro-3-(difluoromethyl)sulfolane,5-fluoro-3-(difluoromethyl)sulfolane,2,2-difluoro-3-(difluoromethyl)sulfolane,2,3-difluoro-3-(difluoromethyl)sulfolane,2,4-difluoro-3-(difluoromethyl)sulfolane,2,5-difluoro-3-(difluoromethyl)sulfolane,3,4-difluoro-3-(difluoromethyl)sulfolane,3,5-difluoro-3-(difluoromethyl)sulfolane,4,4-difluoro-3-(difluoromethyl)sulfolane,4,5-difluoro-3-(difluoromethyl)sulfolane,5,5-difluoro-3-(difluoromethyl)sulfolane,2,2,3-trifluoro-3-(difluoromethyl)sulfolane,2,2,4-trifluoro-3-(difluoromethyl)sulfolane,2,2,5-trifluoro-3-(difluoromethyl)sulfolane,2,3,4-trifluoro-3-(difluoromethyl)sulfolane,2,3,5-trifluoro-3-(difluoromethyl)sulfolane,2,4,4-trifluoro-3-(difluoromethyl)sulfolane,2,4,5-trifluoro-3-(difluoromethyl)sulfolane,2,5,5-trifluoro-3-(difluoromethyl)sulfolane,3,4,4-trifluoro-3-(difluoromethyl)sulfolane,3,4,5-trifluoro-3-(difluoromethyl)sulfolane,4,4,5-trifluoro-3-(difluoromethyl)sulfolane,4,5,5-trifluoro-3-(difluoromethyl)sulfolane,2,2,3,4-tetrafluoro-3-(difluoromethyl)sulfolane,2,2,3,5-tetrafluoro-3-(difluoromethyl)sulfolane,2,2,4,4-tetrafluoro-3-(difluoromethyl)sulfolane,2,2,4,5-tetrafluoro-3-(difluoromethyl)sulfolane,2,2,5,5-tetrafluoro-3-(difluoromethyl)sulfolane,2,3,4,4-tetrafluoro-3-(difluoromethyl)sulfolane,2,3,4,5-tetrafluoro-3-(difluoromethyl)sulfolane,2,3,5,5-tetrafluoro-3-(difluoromethyl)sulfolane,3,4,4,5-tetrafluoro-3-(difluoromethyl)sulfolane,3,4,5,5-tetrafluoro-3-(difluoromethyl)sulfolane,4,4,5,5-tetrafluoro-3-(difluoromethyl)sulfolane,2,2,3,4,4-pentafluoro-3-(difluoromethyl)sulfolane,2,2,3,4,5-pentafluoro-3-(difluoromethyl)sulfolane,2,2,3,5,5-pentafluoro-3-(difluoromethyl)sulfolane,2,3,4,4,5-pentafluoro-3-(difluoromethyl)sulfolane,2,3,4,5,5-pentafluoro-3-(difluoromethyl)sulfolane,2,2,3,4,4,5-hexafluoro-3-(difluoromethyl)sulfolane,2,2,3,4,5,5-hexafluoro-3-(difluoromethyl)sulfolane,2,3,4,4,5,5-hexafluoro-3-(difluoromethyl)sulfolane, andheptafluoro-3-(difluoromethyl)sulfolane, and the like.

Examples of sulfolane derivatives having a trifluoroalkyl substituentand a fluorine atom include

2-fluoro-3-(trifluoromethyl)sulfolane,3-fluoro-3-(trifluoromethyl)sulfolane,4-fluoro-3-(trifluoromethyl)sulfolane,5-fluoro-3-(trifluoromethyl)sulfolane,2,2-difluoro-3-(trifluoromethyl)sulfolane,2,3-difluoro-3-(trifluoromethyl)sulfolane,2,4-difluoro-3-(trifluoromethyl)sulfolane,2,5-difluoro-3-(trifluoromethyl)sulfolane,3,4-difluoro-3-(trifluoromethyl)sulfolane,3,5-difluoro-3-(trifluoromethyl)sulfolane,4,4-difluoro-3-(trifluoromethyl)sulfolane,4,5-difluoro-3-(trifluoromethyl)sulfolane,5,5-difluoro-3-(trifluoromethyl)sulfolane,2,2,3-trifluoro-3-(trifluoromethyl)sulfolane,2,2,4-trifluoro-3-(trifluoromethyl)sulfolane,2,2,5-trifluoro-3-(trifluoromethyl)sulfolane,2,3,4-trifluoro-3-(trifluoromethyl)sulfolane,2,3,5-trifluoro-3-(trifluoromethyl)sulfolane,2,4,4-trifluoro-3-(trifluoromethyl)sulfolane,2,4,5-trifluoro-3-(trifluoromethyl)sulfolane,2,5,5-trifluoro-3-(trifluoromethyl)sulfolane,3,4,4-trifluoro-3-(trifluoromethyl)sulfolane,3,4,5-trifluoro-3-(trifluoromethyl)sulfolane,4,4,5-trifluoro-3-(trifluoromethyl)sulfolane,4,5,5-trifluoro-3-(trifluoromethyl)sulfolane,2,2,3,4-tetrafluoro-3-(trifluoromethyl)sulfolane,2,2,3,5-tetrafluoro-3-(trifluoromethyl)sulfolane,2,2,4,4-tetrafluoro-3-(trifluoromethyl)sulfolane,2,2,4,5-tetrafluoro-3-(trifluoromethyl)sulfolane,2,2,5,5-tetrafluoro-3-(trifluoromethyl)sulfolane,2,3,4,4-tetrafluoro-3-(trifluoromethyl)sulfolane,2,3,4,5-tetrafluoro-3-(trifluoromethyl)sulfolane,2,3,5,5-tetrafluoro-3-(trifluoromethyl)sulfolane,3,4,4,5-tetrafluoro-3-(trifluoromethyl)sulfolane,3,4,5,5-tetrafluoro-3-(trifluoromethyl)sulfolane,4,4,5,5-tetrafluoro-3-(trifluoromethyl)sulfolane,2,2,3,4,4-pentafluoro-3-(trifluoromethyl)sulfolane,2,2,3,4,5-pentafluoro-3-(trifluoromethyl)sulfolane,2,2,3,5,5-pentafluoro-3-(trifluoromethyl)sulfolane,2,3,4,4,5-pentafluoro-3-(trifluoromethyl)sulfolane,2,3,4,5,5-pentafluoro-3-(trifluoromethyl)sulfolane,2,2,3,4,4,5-hexafluoro-3-(trifluoromethyl)sulfolane,2,2,3,4,5,5-hexafluoro-3-(trifluoromethyl)sulfolane,2,3,4,4,5,5-hexafluoro-3-(trifluoromethyl)sulfolane, andheptafluoro-3-(trifluoromethyl)sulfolane, and the like.

More preferred of the sulfolane compounds enumerated above are

sulfolane, 2-methylsulfolane, 3-methylsulfolane, 2,2-dimethylsulfolane,3,3-dimethylsulfolane, 2,3-dimethylsulfolane, 2,4-dimethylsulfolane,2,5-dimethylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane,2-fluoro-3-methylsulfolane, 3-fluoro-3-methylsulfolane,4-fluoro-3-methylsulfolane, 5-fluoro-3-methylsulfolane,2-fluoro-2-methylsulfolane, 3-fluoro-2-methylsulfolane,4-fluoro-2-methylsulfolane, 5-fluoro-2-methylsulfolane,2-fluoro-2,4-dimethylsulfolane, 3-fluoro-2,4-dimethylsulfolane,4-fluoro-2,4-dimethylsulfolane, and 5-fluoro-2,4-dimethylsulfolane.

Especially preferred are

sulfolane, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane,3-fluorosulfolane, 2-fluoro-3-methylsulfolane,3-fluoro-3-methylsulfolane, 4-fluoro-3-methylsulfolane,5-fluoro-3-methylsulfolane, and the like.

In case where a cyclic sulfone compound which has been excessivelyalkyl-substituted is used, the result is an increase in the coefficientof viscosity and this causes a decrease in electrical conductivity. Incase where a cyclic sulfone compound which has been excessivelyfluorinated is used, this compound used in a nonaqueous-electrolytebattery has reduced chemical stability or reduced solubility in othersolvents. There are hence cases where it is difficult to sufficientlyproduce the effects of the invention.

Any one of the cyclic sulfone compounds enumerated above may beincorporated alone into nonaqueous electrolyte 4 of the invention, orany desired combination of two or more thereof in any desired proportionmay be used. Processes for production also are not particularly limited,and a known process selected at will can be used to produce the cyclicsulfone compound.

It is desirable that the cyclic sulfone compound should be incorporatedinto the nonaqueous electrolyte 4 of the invention in a concentrationwhich is generally 10% by volume or higher, preferably 15% by volume orhigher, more preferably 20% by volume or higher, and is generally 70% byvolume or lower, preferably 60% by volume or lower, more preferably 50%by volume or lower, based on the whole nonaqueous solvent in theelectrolyte. When the concentration thereof is lower than the lowerlimit of that range and this nonaqueous electrolyte 4 of the inventionis used in a nonaqueous-electrolyte battery, there are cases where thisnonaqueous-electrolyte battery is less apt to have the effect ofsufficiently improving in safety. In case where the concentrationthereof is higher than the upper limit of that range, there is atendency that the nonaqueous electrolyte comes to have an increasedcoefficient of viscosity and this results in a decrease in electricalconductivity. Especially when this nonaqueous-electrolyte battery ischarged/discharged at a high current density, there are cases wherecharge/discharge capacity retentivity decreases.

<1-3. “Compound Having Coefficient of Viscosity at 25° C. of 1.5 mPa·sor lower”>

It is essential that nonaqueous electrolyte 4 of the invention shouldcontain at least one “compound having a coefficient of viscosity at 25°C. of 1.5 mPa·s or lower”. It is preferred that the “compound having acoefficient of viscosity at 25° C. of 1.5 mPa·s or lower” should be atleast one compound selected from the group consisting of acycliccarbonates, acyclic carboxylic acid esters, acyclic ethers, and cyclicethers, from the standpoint of battery characteristics in the case ofuse in a nonaqueous-electrolyte battery.

The acyclic carbonates preferably are ones having 3-7 carbon atoms. Theacyclic carboxylic acid esters preferably are ones having 3-7 carbonatoms. The acyclic ethers preferably are ones having 3-10 carbon atoms.The cyclic ethers preferably are ones having 3-6 carbon atoms.

Examples of the acyclic carbonates having 3-7 carbon atoms includedimethyl carbonate, diethyl carbonate, di-n-propyl carbonate,diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methylcarbonate, methyl n-propyl carbonate, n-butyl methyl carbonate, isobutylmethyl carbonate, t-butyl methyl carbonate, ethyl n-propyl carbonate,n-butyl ethyl carbonate, isobutyl ethyl carbonate, and t-butyl ethylcarbonate, and the like.

Examples of the acyclic carboxylic acid esters having 3-7 carbon atomsinclude methyl acetate, ethyl acetate, n-propyl acetate, isopropylacetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methylpropionate, ethyl propionate, n-propyl propionate, isopropyl propionate,n-butyl propionate, isobutyl propionate, t-butyl propionate, methylbutyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methylisobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropylisobutyrate, and the like.

Examples of the acyclic ethers having 3-10 carbon atoms include diethylether, di-n-propyl ether, di-n-butyl ether, dimethoxymethane,dimethoxyethane, diethoxymethane, diethoxyethane, ethoxymethoxymethane,ethoxymethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycoldi-n-butyl ether, and diethylene glycol dimethyl ether, and the like.

Examples of the cyclic ethers having 3-6 carbon atoms includetetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran,1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, and1,4-dioxane, and the like.

Preferred of the examples of the “compound having a coefficient ofviscosity at 25° C. of 1.5 mPa·s or lower” enumerated above are dimethylcarbonate, diethyl carbonate, di-n-propyl carbonate, diisopropylcarbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, methyln-propyl carbonate, diethyl ether, di-n-propyl ether, di-n-butyl ether,dimethoxymethane, dimethoxyethane, diethoxymethane, diethoxyethane,ethoxymethoxymethane, ethoxymethoxyethane, tetrahydrofuran,2-methyltetrahydrofuran, 1,3-dioxane, 2-methyl-1,3-dioxane,4-methyl-1,3-dioxane, 1,4-dioxane, methyl acetate, ethyl acetate,n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate,n-propyl propionate, n-butyl propionate, methyl butyrate, ethylbutyrate, n-propyl butyrate, methyl isobutyrate, and ethyl isobutyrate.

Preferred of these is dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dimethoxyethane, ethoxymethoxyethane, tetrahydrofuran,2-methyltetrahydrofuran, 1,3-dioxane, 1,4-dioxane, methyl acetate, ethylacetate, methyl propionate, ethyl propionate, methyl butyrate, ethylbutyrate, methyl isobutyrate, or ethyl isobutyrate. Especially preferredof these, from the standpoint of decomposition gas evolution duringhigh-temperature battery storage, is dimethyl carbonate, diethylcarbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methylpropionate, ethyl propionate, methyl butyrate, ethyl butyrate, methylisobutyrate, or ethyl isobutyrate.

Incidentally, the coefficient of viscosity at 25° C. is a value measuredwith any of a capillary viscometer, falling-ball viscometer, andvibration viscometer. When the coefficient of viscosity of the compound,which is a Newtonian fluid, is precisely measured with theseviscometers, the same value is obtained within an error range for themeasurements. However, it is preferred that the coefficient of viscosityshould be measured with a capillary viscometer. Processes for productionalso are not particularly limited, and a known process selected at willcan be used to produce the compound.

Also with respect to the compound having a specific low coefficient ofviscosity explained above, any one of the examples of the compound maybe incorporated alone into nonaqueous electrolyte 4 of the invention orany desired combination of two or more thereof in any desired proportionmay be used. In the case where the “at least one compound selected fromthe group consisting of carbonates having an unsaturated bond,carbonates having a halogen atom, monofluorophosphates, anddifluorophosphates”, which will be described later, has a coefficient ofviscosity at 25° C. of 1.5 mPa·s or lower, then this compound isregarded also as a “compound having a coefficient of viscosity at 25° C.of 1.5 mPa·s or lower”. In this case, when this compound is used in aproportion of 30% by volume or higher based on the whole nonaqueouselectrolyte, the coefficient of viscosity of the nonaqueous electrolytecan be reduced to a value within a range advantageous for thehigh-current-density charge/discharge characteristics of the battery.When the proportion thereof is 8% by mass or lower based on the wholenonaqueous electrolyte, an electrode surface coating film having highlithium ion conductivity can be formed.

In the invention, the content of the “compound having a coefficient ofviscosity at 25° C. of 1.5 mPa·s or lower” is not particularly limited.However, it is desirable to incorporate this compound in a concentrationof generally 30% by volume or higher, preferably 40% by volume orhigher, more preferably 50% by volume or higher, based on the wholenonaqueous solvent in the nonaqueous electrolyte. In case where theconcentration thereof is lower than the lower limit, there is a tendencythat the nonaqueous electrolyte comes to have an increased coefficientof viscosity and this results in a decrease in electrical conductivity.In particular, there are cases where the nonaqueous-electrolyte batteryhas reduced heavy-current discharge characteristics. It is alsodesirable to incorporate the compound in a concentration of generally90% by volume or lower, preferably 85% by volume or lower, morepreferably 80% by volume or lower. In case where the concentrationthereof exceeds the upper limit of that range, there is a tendency thatthis nonaqueous electrolyte 4 of the invention has a reducedpermittivity and this results in a decrease in electrical conductivity.In particular, there are cases where the nonaqueous-electrolyte batteryhas reduced heavy-current discharge characteristics.

The nonaqueous solvent in nonaqueous electrolyte 4 according to theinvention may include a highly polar solvent such as, e.g., a cycliccarbonate, so long as this does not lessen the effects of the invention.Preferred examples of such mixed solvents include a combination composedmainly of a sulfolane compound, an acyclic carbonate, and a cycliccarbonate, a combination composed mainly of a sulfolane compound, anacyclic ether, and a cyclic carbonate, and a combination composed mainlyof a sulfolane compound, an acyclic ester, and a cyclic carbonate.

One preferred combination for constituting a nonaqueous solvent is acombination consisting mainly of at least one sulfolane compound, atleast one acyclic carbonate, and at least one cyclic carbonate. Inparticular, this combination is one in which the total proportion of thesulfolane compound and the cyclic carbonate to the nonaqueous solvent is15% by volume or higher, preferably 20% by volume or higher, morepreferably 25% by volume or higher, and is generally 70% by volume orlower, preferably 60% by volume or lower, more preferably 50% by volumeor lower, the proportion of the volume of the cyclic carbonate to thesum of the sulfolane compound and the cyclic carbonate is 5% or higher,preferably 10% by volume or higher, more preferably 15% by volume orhigher, and is generally 90% by volume or lower, preferably 80% byvolume or lower, more preferably 70% by volume or lower, and theproportion of the acyclic carbonate to the nonaqueous electrolyte isgenerally 30% by volume or higher, preferably 40% by volume or higher,more preferably 50% by volume or higher, and is generally 90% by volumeor lower, preferably 85% by volume or lower, more preferably 80% byvolume or lower. Use of such combination of nonaqueous solvents ispreferred because the battery fabricated with this combination has animproved balance between cycle characteristics and high-temperaturestorability (in particular, residual capacity and high-load dischargecapacity after high-temperature storage).

Examples of the preferred combination including at least one sulfolanecompound, at least one cyclic carbonate, and at least one acycliccarbonate include: sulfolane, ethylene carbonate, and dimethylcarbonate; sulfolane, ethylene carbonate, and diethyl carbonate;sulfolane, ethylene carbonate, and ethyl methyl carbonate; sulfolane,ethylene carbonate, dimethyl carbonate, and diethyl carbonate;sulfolane, ethylene carbonate, dimethyl carbonate, and ethyl methylcarbonate; sulfolane, ethylene carbonate, diethyl carbonate, and ethylmethyl carbonate; and sulfolane, ethylene carbonate, dimethyl carbonate,diethyl carbonate, and ethyl methyl carbonate, and the like.

Combinations obtained by further adding propylene carbonate to thosecombinations including sulfolane, ethylene carbonate, and one or moreacyclic carbonates are also included in preferred combinations.

In the case where propylene carbonate is contained, the volume ratio ofthe ethylene carbonate to the propylene carbonate is preferably from99:1 to 40:60, especially preferably from 95:5 to 50:50. Furthermore,the proportion of the propylene carbonate to the whole nonaqueoussolvent of the electrolyte may be regulated to 0.1% by volume or higher,preferably 1% by volume or higher, more preferably 2% by volume orhigher, and the upper limit thereof may be regulated to generally 20% byvolume or lower, preferably 8% by volume or lower, more preferably 5% byvolume or lower. Incorporation of propylene carbonate in an amountwithin that range is preferred because this incorporation brings abouteven better low-temperature characteristics while maintaining theproperties of the combination of sulfolane, ethylene carbonate, and oneor more dialkyl carbonates.

In this description, the values of the volumes of nonaqueous solventsare ones measured at 25° C. However, in the case of a nonaqueous solventwhich is solid at 25° C., such as, e.g., ethylene carbonate, the valuemeasured at the melting point is used.

<1-4. “At Least One Compound Selected from Group Consisting OfCarbonates Having Unsaturated Bond(s), Carbonates Having HalogenAtom(s), Monofluorophosphates, and Difluorophosphates”>

Nonaqueous electrolyte 4 of the invention contains “at least onecompound selected from the group consisting of carbonates having anunsaturated bond, carbonates having a halogen atom,monofluorophosphates, and difluorophosphates” (hereinafter sometimesreferred to as “specific compound(s)”) besides the ingredients describedabove. Each of these specific compounds has the ability to form aninterface-protective coating film. There is hence a conception by whichthe specific compounds as components of an electrolyte can be classifiedin the same group.

<1-4-1. Carbonates Having Unsaturated Bond(s)>

The carbonates having an unsaturated bond (hereinafter sometimesreferred to as “unsaturated carbonates”) are not particularly limited solong as they are carbonates having one or more carbon-carbon unsaturatedbonds, such as carbon-carbon double bonds or carbon-carbon triple bonds.Any desired unsaturated carbonate can be used. Incidentally, carbonateshaving one or more aromatic rings are also included in the carbonateshaving an unsaturated bond.

With respect to the unsaturated carbonates in nonaqueous electrolyte 4,the same explanation as that given above with regard to nonaqueouselectrolyte 1 applies.

<1-4-2. Carbonates Having Halogen Atom(s)>

On the other hand, the carbonates having a halogen atom (hereinaftersometimes referred to as “halogenated carbonates”) are not particularlylimited so long as they are carbonates having a halogen atom. Anydesired halogenated carbonate can be used. With respect to thehalogenated carbonates in nonaqueous electrolyte 4, the same explanationas that given above with regard to nonaqueous electrolytes 1 and 2applies.

It is also preferred to use a carbonate having both an unsaturated bondand a halogen atom (this carbonate is hereinafter sometimes referred toas “halogenated unsaturated carbonate”). This halogenated unsaturatedcarbonate is not particularly limited, and any desired halogenatedunsaturated carbonate can be used unless the effects of the inventionare considerably lessened thereby. With respect to the halogenatedunsaturated carbonate in nonaqueous electrolyte 4, the same explanationas that given above with regard to nonaqueous electrolyte 2 applies.

The “carbonates having an unsaturated bond” and the “carbonates having ahalogen atom” are hereinafter inclusively referred to as “specificcarbonates”. The specific carbonates are not particularly limited inmolecular weight, and may have any desired molecular weight unless theeffects of the invention are considerably lessened thereby. However, themolecular weight thereof is generally 50 or higher, preferably 80 orhigher, and is generally 250 or lower, preferably 150 or lower. When themolecular weight thereof is too high, there are cases where suchspecific carbonates have reduced solubility in the nonaqueouselectrolyte, making it difficult to sufficiently produce the effects ofthe invention. Processes for producing specific carbonates also are notparticularly limited, and a known process selected at will can be usedto produce the carbonates.

Any one specific carbonate may be incorporated alone into nonaqueouselectrolyte 4 of the invention, or any desired combination of two ormore specific carbonates in any desired proportion may be incorporated.The amount of the specific carbonate to be incorporated into thenonaqueous electrolyte 4 of the invention is not limited, and thespecific carbonate may be incorporated in any desired amount unless theeffects of the invention are considerably lessened thereby. However, itis desirable that the specific carbonate should be incorporated in aconcentration which is generally 0.01% by mass or higher, preferably0.1% by mass or higher, more preferably 0.3% by mass or higher, and isgenerally 8% by mass or lower, preferably 5% by mass or lower, morepreferably 3% by mass or lower, based on the whole nonaqueouselectrolyte 4 of the invention. When the proportion thereof is lowerthan the lower limit of that range and this nonaqueous electrolyte 4 ofthe invention is used in a nonaqueous-electrolyte battery, there arecases where this nonaqueous-electrolyte battery is less apt to have theeffect of sufficiently improving in cycle characteristics. On the otherhand, in case where the proportion of the specific carbonate is toohigh, use of this nonaqueous electrolyte 4 of the invention in anonaqueous-electrolyte battery tends to result in reducedhigh-temperature storability of this nonaqueous-electrolyte battery. Inparticular, there are cases where gas evolution is enhanced anddischarge capacity retentivity decreases.

<1-4-3. Monofluorophosphates and Difluorophosphates>

With respect to the “monofluorophosphates and difluorophosphates” foruse in invention 4, the kinds and contents thereof, places where thesalts exist, methods of analysis, production process, etc. are the sameas those described above with regard to nonaqueous electrolyte 1.

Nonaqueous electrolyte 4 of the invention can contain “other compounds”so long as this does not lessen the effects of the invention. Examplesof the “other compounds” include various compounds includingconventionally known overcharge inhibitors and aids.

<1-5. Overcharge Inhibitor>

By incorporating an overcharge inhibitor, the battery can be inhibitedfrom rupturing/firing upon overcharge, etc. With respect to theovercharge inhibitor in nonaqueous electrolyte 4, the same explanationas that given above with regard to nonaqueous electrolyte 1 applies.Preferred examples thereof include the following.

Examples of the overcharge inhibitor include: aromatic compounds such asbiphenyl, alkylbiphenyls, terphenyl, partly hydrogenated terphenyls,cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, anddibenzofuran; products of the partial fluorination of these aromaticcompounds, such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, andp-cyclohexylfluorobenzene; and fluorine-containing anisole compoundssuch as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole,and 3,5-difluoroanisole. Preferred of these are aromatic compounds suchas biphenyl, alkylbiphenyls, terphenyl, partly hydrogenated terphenyls,cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, anddibenzofuran. Two or more of these may be used in combination. In thecase where two or more compounds are used in combination, it isespecially preferred, from the standpoint of a balance betweenovercharge-inhibiting properties and high-temperature storability, toemploy a combination of cyclohexylbenzene and t-butylbenzene ort-amylbenzene or to use a compound selected from oxygen-free aromaticcompounds such as biphenyl, alkylbiphenyls, terphenyl, partlyhydrogenated terphenyls, cyclohexylbenzene, t-butylbenzene, andt-amylbenzene in combination with a compound selected fromoxygen-containing aromatic compounds such as diphenyl ether anddibenzofuran.

The proportion of the overcharge inhibitor in nonaqueous electrolyte 4is generally 0.1% by mass or higher, preferably 0.2% by mass or higher,especially preferably 0.3% by mass or higher, most preferably 0.5% bymass or higher, based on the whole nonaqueous electrolyte. The upperlimit thereof is generally 5% by mass or lower, preferably 3% by mass orlower, especially preferably 2% by mass or lower. In case where theconcentration thereof is lower than the lower limit, the overchargeinhibitor produces almost no effect. Conversely, too high concentrationsthereof tend to result in a decrease in battery characteristics, e.g.,high-temperature storability.

<1-6. Aids>

Examples of the aids include: carbonate compounds such as erythritancarbonate, spiro-bis-dimethylene carbonate, and methoxyethyl methylcarbonate; carboxylic acid anhydrides such as succinic anhydride,glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconicanhydride, itaconic anhydride, diglycolic anhydride,cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylicdianhydride, and phenylsuccinic anhydride; spiro compounds such as2,4,8,10-tetraoxaspiro[5.5]undecane and3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane; sulfur-containingcompounds such as ethylene sulfite, 1,3-propanesultone,1,4-butanesultone, methyl methanesulfonate, ethyl methanesulfonate,busulfan, sulfolene, dimethyl sulfone, diphenyl sulfone,N,N-dimethylmethanesulfonamide, and N,N-diethylmethanesulfonamide;nitrogen-containing compounds such as 1-methyl-2-pyrrolinone,1-methyl-2-piperidone, 3-methyl-2-oxazolidinone,1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; hydrocarboncompounds such as heptane, octane, nonane, decane, and cycloheptane; andfluorine-containing aromatic compounds such as fluorobenzene,difluorobenzene, hexafluorobenzene, and benzotrifluoride. Two or more ofthese aids may be used in combination.

The proportion of these aids in nonaqueous electrolyte 4 is generally0.01% by mass or higher, preferably 0.1% by mass or higher, especiallypreferably 0.2% by mass or higher, based on the whole nonaqueouselectrolyte 4. The upper limit thereof is generally 5% by mass or lower,preferably 3% by mass or lower, especially preferably 1% by mass orlower. By adding those aids, capacity retentivity after high-temperaturestorage and cycle characteristics can be improved. In case where theconcentration thereof is lower than the lower limit, the aids producealmost no effect. Conversely, too high concentrations thereof tend toresult in a decrease in battery characteristics, e.g., high-loaddischarge characteristics.

<1-7. Preparation of Nonaqueous Electrolyte>

Nonaqueous electrolyte 4 according to the invention can be prepared bymixing an electrolyte, a cyclic sulfone compound, “a compound having acoefficient of viscosity at 25° C. of 1.5 mPa·s or lower”, and thespecific compound optionally together with “other compounds” to dissolvethese ingredients in each other. It is preferred that in preparingnonaqueous electrolyte 4, each raw material should be dehydratedbeforehand in order to reduce the water content of the electrolyte to beobtained. It is desirable to dehydrate each raw material to generally 50ppm or lower, preferably 30 ppm or lower, especially preferably 10 ppmor lower. It is also possible to conduct dehydration, deacidification,and the like after the preparation of an electrolyte.

Nonaqueous electrolyte 4 of the invention is suitable for use as anelectrolyte for nonaqueous-electrolyte batteries, in particular, forsecondary batteries, e.g., lithium secondary batteries.Nonaqueous-electrolyte battery 4, which employs the electrolyte of theinvention, is explained below.

[2. Nonaqueous-Electrolyte Battery]

Nonaqueous-electrolyte battery 4 of the invention includes: a negativeelectrode and a positive electrode which are capable of occluding andreleasing ions; and the nonaqueous electrolyte 4 of the invention.

<2-1. Battery Constitution>

Nonaqueous-electrolyte secondary battery 4 of the invention may have thesame battery constitution as that described above with regard tononaqueous-electrolyte secondary battery 1.

<2-2. Nonaqueous Electrolyte>

As the nonaqueous electrolyte, the nonaqueous electrolyte 4 of theinvention described above is used. Incidentally, a mixture of nonaqueouselectrolyte 4 of the invention and another nonaqueous electrolyte may beused so long as this is not counter to the spirit of invention 4.

<2-3. Negative Electrode>

The negative electrode of nonaqueous-electrolyte secondary battery 4 maybe the same as the negative electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-4. Positive Electrode>

The positive electrode of nonaqueous-electrolyte secondary battery 4 maybe the same as the positive electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-5. Separator>

The separator of nonaqueous-electrolyte secondary battery 4 may be thesame as the separator described above with regard tononaqueous-electrolyte secondary battery 1.

<2-6. Battery Design>

The battery design of nonaqueous-electrolyte secondary battery 4 may bethe same as the battery design described above with regard tononaqueous-electrolyte secondary battery 1.

Nonaqueous-electrolyte secondary battery 5 of the invention isconstituted of a nonaqueous electrolyte and a positive electrode and anegative electrode which both are capable of occluding and releasinglithium. Nonaqueous-electrolyte secondary battery 5 of the invention maybe equipped with other constitutions.

I. Nonaqueous Electrolyte Embodiment 5-1

Nonaqueous electrolyte 5 of the invention is a nonaqueous electrolytewhich includes a nonaqueous organic solvent and a lithium salt dissolvedtherein, and is characterized in that the nonaqueous organic solventcontains a cyclic polyamine compound and/or a cyclic polyamide compoundand further contains at least one compound selected from the groupconsisting of unsaturated carbonates, fluorine-containing carbonates,monofluorophosphates, and difluorophosphates. This electrolyte isreferred to as “embodiment 5-1”.

[1. Cyclic Polyamine Compound]

[1-1. Kind]

The cyclic polyamine compound which may be contained in nonaqueouselectrolyte 5 of the invention (hereinafter suitably referred to as“cyclic polyamine compound of invention 5”) is any of cyclic compoundshaving a structure formed by the condensation of one or more amines andderivatives of such cyclic compounds. Namely, the cyclic polyaminecompound is any of cyclic compounds including two or more nitrogen atomsbonded to each other with alkylene groups and derivatives thereof formedby replacing one or more of the hydrogen atoms bonded to the nitrogenatoms with a hydrocarbon group.

The number of the nitrogen atoms constituting the ring is preferably 3or larger, especially preferably 4 or larger, and is preferably 6 orsmaller, especially preferably 4 or smaller. The alkylene groups are notparticularly limited. However, alkylene groups having 2-4 carbon atoms,such as ethylene, methylethylene, propylene, and butylene, arepreferred. Especially preferred is ethylene or propylene. Two or morekinds of alkylene groups may be contained.

Examples of the hydrocarbon group with which the hydrogen bonded to anitrogen atom is replaced include alkyl groups, aryl groups, and aralkylgroups. Preferred of these are alkyl groups. Examples of the alkylgroups include methyl, ethyl, propyl, isopropyl, and butyl. Examples ofthe aryl groups include aryl groups having 6-8 carbon atoms, such asphenyl, p-tolyl, ethylphenyl, and dimethylphenyl. Examples of thearalkyl groups include benzyl and phenethyl.

The molecular weight of the cyclic polyamine compound of invention 5 ispreferably 120 or higher, more preferably 170 or higher, and ispreferably 800 or lower, more preferably 400 or lower, especiallypreferably 300 or lower. When the molecular weight thereof exceeds theupper limit of that range, there are cases where this polyamine compoundis reduced in compatibility with or solubility in the nonaqueouselectrolyte, resulting in a decrease in capacity especially at lowtemperatures.

Examples of the cyclic polyamine compound of invention 5 are shownbelow. However, the cyclic polyamine compound of invention 5 should notbe construed as being limited to the following examples.

Examples of the cyclic polyamine compound of invention 5 include

triazacycloalkanes such as 1,4,7-triazacyclononane,1,4,7-triazacyclodecane, 1,4,8-triazacycloundecane,1,5,9-triazacyclododecane, and 1,6,11-triazacyclopentadecane etc.;

tetraazacycloalkanes such as 1,4,7,10-tetraazacyclododecane (anothername: cyclen), 1,4,7,10-tetraazacyclotridecane,1,4,7,11-tetraazacyclotetradecane, 1,4,8,11-tetraazacyclotetradecane(another name: cyclam), 1,4,8,12-tetraazacyclopentadecane, and1,5,9,13-tetraazacyclohexadecane;pentaazacycloalkanes such as 1,4,7,10,13-pentaazacyclopentadecane and1,4,7,10,13-pentaazacyclohexadecane;hexaazacycloalkanes such as 1,4,7,10,13,16-hexaazacyclooctadecane(another name: hexacyclen) and 1,4,7,10,13,16-hexaazacyclononadecaneetc.;hydrocarbon-group-substituted triazacycloalkanes such as1,4,7-trimethyl-1,4,7-triazacyclononane,2,5,8-trimethyl-1,4,7-triazacyclononane,1,4,7-triethyl-1,4,7-triazacyclononane,1,4,7-triphenyl-1,4,7-triazacyclononane,1,4,7-tribenzyl-1,4,7-triazacyclononane,1,5,9-trimethyl-1,5,9-triazacyclododecane,1,5,9-triethyl-1,5,9-triazacyclododecane,1,5,9-triphenyl-1,5,9-triazacyclododecane, and1,5,9-tribenzyl-1,5,9-triazacyclododecane etc.;hydrocarbon-group-substituted tetraazacycloalkanes such as2,5,8,11-tetramethyl-1,4,7,10-tetraazacyclododecane,1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane,1,4,7,10-tetraethyl-1,4,7,10-tetraazacyclododecane,1,4,7,10-tetraphenyl-1,4,7,10-tetraazacyclododecane,1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane,1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane,1,4,8,11-tetraethyl-1,4,8,11-tetraazacyclotetradecane,1,4,8,11-tetraphenyl-1,4,8,11-tetraazacyclotetradecane,1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane,1,4,8,12-tetramethyl-1,4,8,12-tetraazacyclopentadecane,1,4,8,12-tetraethyl-1,4,8,12-tetraazacyclopentadecane,1,4,8,12-tetraphenyl-1,4,8,12-tetraazacyclopentadecane, and1,4,8,12-tetrabenzyl-1,4,8,12-tetraazacyclopentadecane; andhydrocarbon-group-substituted hexaazacycloalkanes such as1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane,1,4,7,10,13,16-hexaethyl-1,4,7,10,13,16-hexaazacyclooctadecane,1,4,7,10,13,16-hexaphenyl-1,4,7,10,13,16-hexaazacyclooctadecane, and1,4,7,10,13,16-hexabenzyl-1,4,7,10,13,16-hexaazacyclooctadecane, and thelike.

Preferred of these are

triazacycloalkanes such as 1,4,7-triazacyclononane and1,5,9-triazacyclododecane; tetraazacycloalkanes such as1,4,7,10-tetraazacyclododecane (another name: cyclen),1,4,8,11-tetraazacyclotetradecane (another name: cyclam), and1,4,8,12-tetraazacyclopentadecane; and1,4,7,10,13,16-hexaazacyclooctadecane (another name: hexacyclen) andmethyl-substituted azacycloalkanes such as1,4,7-trimethyl-1,4,7-triazacyclononane,1,5,9-trimethyl-1,5,9-triazacyclododecane,1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane,1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, and1,4,8,12-tetramethyl-1,4,8,12-tetraazacyclopentadecane, and the like.

Especially preferred of these are

triazacycloalkanes such as 1,4,7-triazacyclononane and1,5,9-triazacyclododecane;

tetraazacycloalkanes such as 1,4,7,10-tetraazacyclododecane (anothername: cyclen), 1,4,8,11-tetraazacyclotetradecane (another name: cyclam),and 1,4,8,12-tetraazacyclopentadecane; and

methyl-substituted tetraazacycloalkanes such as1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, and the like.

One cyclic polyamine compound of invention 5 may be used alone, or anydesired combination of two or more cyclic polyamine compounds ofinvention 5 in any desired proportion may be used.

These cyclic polyamine compounds have a molecular weight which is notexcessively high. These compounds readily dissolve in nonaqueous organicsolvents and partly undergo oxidation at the positive electrode. Uponthis oxidation, the compounds form a stable coating film on the positiveelectrode. Because of this, the nonaqueous-electrolyte secondary batteryemploying the nonaqueous electrolyte containing any of these cyclicpolyamine compounds has improved continuous-charge characteristics.

[1-2. Composition]

The content of the cyclic polyamine compound of invention 5 is notparticularly limited so long as the compound dissolves in the nonaqueoussolvent which will be described later. However, the cyclic polyaminecompound is contained in such an amount that the content thereof isgenerally 0.001% by mass or higher, preferably 0.01% by mass or higher,and is generally 5% by mass or lower, preferably 1% by mass or lower,especially preferably 0.2% by mass or lower, based on the wholenonaqueous electrolyte. When the content thereof is lower than the lowerlimit of that range, there are cases where the effects of invention 5are hardly produced. When the content thereof exceeds the upper limit,there are cases where the nonaqueous organic solvent includingcarbonates comes to undergo a decomposition reaction catalyzed by thecyclic polyamine compound, resulting in a decrease in batterycharacteristics such as rate characteristics. In the case of using twoor more cyclic polyamine compounds of invention 5 in combination, thecyclic polyamine compounds of invention 5 are used so that the totalconcentration thereof is within the range shown above.

[2. Cyclic Polyamide Compound]

[2-1. Kind]

The cyclic polyamide compound which may be contained in nonaqueouselectrolyte 5 of the invention (hereinafter suitably referred to as“cyclic polyamide compound of invention 5”) is a compound having two ormore amide bonds (—NHCO—) in the ring framework. The number of the amidebonds constituting the ring is preferably 2 or larger and is preferably6 or smaller, especially preferably 4 or smaller. A cyclic polyamidecompound having two amide bonds can be synthesized, for example, by thereaction of an acyclic polyamine compound with a malonic acidderivative. Cyclic polyamide compounds having three or more amide bondscan be synthesized, for example, by the cyclization polymerizationreaction of various amino acids.

The molecular weight of the cyclic polyamide compound of invention 5 ispreferably 160 or higher, more preferably 200 or higher, and ispreferably 800 or lower, more preferably 600 or lower, especiallypreferably 500 or lower. When the molecular weight thereof exceeds theupper limit of that range, there are cases where the cyclic polyamidecompound of invention 5 is reduced in compatibility with or solubilityin nonaqueous organic solvents and this may cause a decrease in capacityespecially at low temperatures.

Examples of the cyclic polyamide compound of invention 5 are shownbelow. However, the cyclic polyamide compound of invention 5 should notbe construed as being limited to the following examples.

Examples of the cyclic polyamide compound of invention 5 which has twoamide bonds include

(substituted) triazacycloalkanediones such as1,4,7-triazacyclodecane-8,10-dione,9-methyl-1,4,7-triazacyclodecane-8,10-dione,9,9′-dimethyl-1,4,7-triazacyclodecane-8,10-dione,9-ethyl-1,4,7-triazacyclodecane-8,10-dione,9-phenyl-1,4,7-triazacyclodecane-8,10-dione,9-benzyl-1,4,7-triazacyclodecane-8,10-dione,1,5,9-triazacyclododecane-6,8-dione,7-methyl-1,5,9-triazacyclododecane-6,8-dione,7,7′-methyl-1,5,9-triazacyclododecane-6,8-dione,7-ethyl-1,5,9-triazacyclododecane-6,8-dione,7-phenyl-1,5,9-triazacyclododecane-6,8-dione, and7-benzyl-1,5,9-triazacyclododecane-6,8-dione;(substituted) tetraazacycloalkanediones such as1,4,7,10-tetraazacyclotridecane-11,13-dione,12-methyl-1,4,7,10-tetraazacyclotridecane-11,13-dione,12,12′-dimethyl-1,4,7,10-tetraazacyclotridecane-11,13-dione,12-ethyl-1,4,7,10-tetraazacyclotridecane-11,13-dione,12-phenyl-1,4,7,10-tetraazacyclotridecane-11,13-dione,12-benzyl-1,4,7,10-tetraazacyclotridecane-11,13-dione,1,4,8,11-tetraazacyclotetradecane-5,7-dione,6-methyl-1,4,8,11-tetraazacyclotetradecane-5,7-dione,6,6′-dimethyl-1,4,8,11-tetraazacyclotetradecane-5,7-dione,6-ethyl-1,4,8,11-tetraazacyclotetradecane-5,7-dione,6-phenyl-1,4,8,11-tetraazacyclotetradecane-5,7-dione,6-benzyl-1,4,8,11-tetraazacyclotetradecane-5,7-dione,1,4,8,12-tetraazacyclopentadecane-9,11-dione,10-methyl-1,4,8,12-tetraazacyclopentadecane-9,11-dione,10,10′-dimethyl-1,4,8,12-tetraazacyclopentadecane-9,11-dione,10-ethyl-1,4,8,12-tetraazacyclopentadecane-9,11-dione,10-phenyl-1,4,8,12-tetraazacyclopentadecane-9,11-dione, and10-benzyl-1,4,8,12-tetraazacyclopentadecane-9,11-dione; and(substituted) tetraazacycloalkanediones such as1,4,7,10,13,16-hexaazacyclononadecane-17,19-dione,18-methyl-1,4,7,10,13,16-hexaazacyclononadecane-17,19-dione,18,18′-diethyl-1,4,7,10,13,16-hexaazacyclononadecane-17,19-dione,18-ethyl-1,4,7,10,13,16-hexaazacyclononadecane-17,19-dione,18-phenyl-1,4,7,10,13,16-hexaazacyclononadecane-17,19-dione, and18-benzyl-1,4,7,10,13,16-hexaazacyclononadecane-17,19-dione, and thelike.

Examples of the cyclic polyamide compound which has three or more amidebonds include

cyclic triamides such as cyclo(-glycyl)₃, cyclo(β-alanyl)3, andcyclo(-prolyl)3;

cyclic tetraamides such as cyclo(-glycyl)4, cyclo(β-alanyl)4,cyclo(β-alanylglycyl-β-alanylglycyl),cyclo(β-alanylprolyl-β-alanylprolyl), cyclo(-glycyl)4, andcyclo(β-alanyl)4; and

cyclic hexaamides such as cyclo(-glycyl)6 and cyclo(-prolyl-glycyl)3,and the like.

Preferred of these are

triazacycloalkanediones such as 1,4,7-triazacyclodecane-8,10-dione and1,5,9-triazacyclododecane-6,8-dione;

tetraazacycloalkanediones such as1,4,7,10-tetraazacyclotridecane-11,13-dione,1,4,8,11-tetraazacyclotetradecane-5,7-dione, and1,4,8,12-tetraazacyclopentadecane-9,11-dione;

hexaamides such as cyclo(β-alanylglycyl-β-alanylglycyl) andcyclo(-prolyl-glycyl)3; and the like.

Especially preferred of these are

1,4,7,10-tetraazacyclotridecane-11,13-dione,1,4,8,11-tetraazacyclotetradecane-5,7-dione,1,4,8,12-tetraazacyclopentadecane-9,11-dione,cyclo(β-alanylglycyl-β-alanylglycyl), and the like.

One of the polyamide compounds of invention 5 shown above may be usedalone, or any desired combination of two or more thereof in any desiredproportion may be used.

These cyclic polyamide compounds of invention 5 have a molecular weightwhich is not excessively high. These compounds readily dissolve innonaqueous organic solvents and partly undergo oxidation at the positiveelectrode. Upon this oxidation, the compounds form a stable coating filmon the positive electrode. Because of this, the nonaqueous-electrolytesecondary battery employing the nonaqueous electrolyte containing any ofthese cyclic polyamide compounds of invention 5 has improvedcontinuous-charge characteristics.

[2-2. Composition]

The content of the cyclic polyamide compound of invention 5 is notparticularly limited so long as the compound dissolves in the nonaqueoussolvent which will be described later. However, the cyclic polyamidecompound is contained in such an amount that the content thereof isgenerally 0.001% by mass or higher, preferably 0.01% by mass or higher,and is generally 5% by mass or lower, preferably 1% by mass or lower,especially preferably 0.2% by mass or lower, based on the wholenonaqueous electrolyte. When the content thereof is lower than the lowerlimit of that range, there are cases where the effects of invention 5are hardly produced. When the content thereof exceeds the upper limit,there are cases where the coating film formed on the positive electrodehas an increased thickness and higher resistance and this coating filmhence inhibits the movement of lithium (Li) ions, resulting in adecrease in battery characteristics such as rate characteristics. In thecase of using two or more cyclic polyamide compounds of invention 5 incombination, the cyclic polyamide compounds of invention 5 are used sothat the total concentration thereof is within the range shown above.

[3. At Least One Compound Selected from Group Consisting of UnsaturatedCarbonates, Fluorine-Containing Carbonates, Monofluorophosphates, andDifluorophosphates]

Nonaqueous electrolyte 5 of the invention further contains at least onecompound selected from the group consisting of unsaturated carbonates,fluorine-containing carbonates, monofluorophosphates, anddifluorophosphates. These compounds are incorporated, for example, forthe purpose of forming a coating film on the negative electrode toimprove battery characteristics.

[3-1. Kind]

The unsaturated carbonates are not particularly limited so long as theyare carbonates having one or more carbon-carbon unsaturated bonds. Anydesired unsaturated carbonates can be used. Examples thereof includecarbonates having one or more aromatic rings and carbonates having oneor more carbon-carbon unsaturated bonds such as carbon-carbon doublebonds or carbon-carbon triple bonds. The unsaturated carbonates are thesame as those described above with regard to nonaqueous electrolyte 1.

The fluorine-containing carbonates are not limited so long as they arecarbonates having a fluorine atom. Any desired fluorine-containingcarbonates can be used.

Examples thereof include

fluorine-containing cyclic carbonates such as fluoroethylene carbonate,1,1-difluoroethylene carbonate, cis-difluoroethylene carbonate,trans-difluoroethylene carbonate, fluoropropylene carbonate, andtrifluoromethylethylene carbonate; and

fluorine-containing acyclic carbonates such as trifluoromethyl methylcarbonate, trifluoromethyl ethyl carbonate, 2-fluoroethyl methylcarbonate, 2-fluoroethyl ethyl carbonate, 2,2,2-trifluoroethyl methylcarbonate, 2,2,2-trifluoroethyl ethyl carbonate,bis(trifluoromethyl)carbonate, bis(2-fluoroethyl)carbonate, andbis(2,2,2-trifluoroethyl)carbonate, and the like.

Of these,

fluorine-containing cyclic carbonates such as fluoroethylene carbonate,cis-difluoroethylene carbonate, and trans-difluoroethylene carbonate arepreferred because these carbonates form a stable interface-protectivecoating film on the negative electrode.

One fluorine-containing carbonate may be used alone, or any desiredcombination of two or more fluorine-containing carbonates in any desiredproportion may be used.

As the monofluorophosphates and difluorophosphates, any desired ones canbe used. With respect to the “monofluorophosphates anddifluorophosphates” to be used in invention 5 (including all ofembodiment 5-1, embodiment 5-2, and embodiment 5-3), the kinds andcontents thereof, places where the salts exist, methods of analysis,production process, etc., are the same as those described above withregard to nonaqueous electrolyte 1. Especially preferred examplesthereof include lithium monofluorophosphate, sodium monofluorophosphate,potassium monofluorophosphate, lithium difluorophosphate, sodiumdifluorophosphate, and potassium difluorophosphate. Preferred of theseare lithium monofluorophosphate and lithium difluorophosphate. Onemonofluorophosphate or difluorophosphate may be used alone, or anydesired combination of two or more of monofluorophosphates anddifluorophosphates in any desired proportion may be used.

[3-2. Composition]

The concentration of the at least one compound selected from the groupconsisting of unsaturated carbonates, fluorine-containing carbonates,monofluorophosphates, and difluorophosphates in nonaqueous electrolyte 5is generally 0.01% by mass or higher, preferably 0.1% by mass or higher,more preferably 0.3% by mass or higher, and is generally 10% by mass orlower, preferably 7% by mass or lower, more preferably 5% by mass orlower, based on the whole nonaqueous electrolyte. In case where theconcentration thereof is too high, the coating film formed on thenegative electrode has an increased thickness and higher resistance,resulting in a decrease in battery capacity. There also are cases wheregas evolution is enhanced under high-temperature conditions and thisfurther increases resistance to reduce the capacity. When theconcentration thereof is too low, there are cases where the effects ofinvention 5 are not sufficiently produced.

[Function]

Reasons for the preference of the containment of at least one compoundselected from the group consisting of unsaturated carbonates,fluorine-containing carbonates, monofluorophosphates, anddifluorophosphates in nonaqueous electrolyte 5 of the invention areexplained here. However, invention 5 should not be construed as beinglimited by the following reasons. The polyamine compound and/orpolyamide compound of invention 5 is oxidized at the positive electrodeat a less noble potential than the solvent and functions as apositive-electrode-protective coating film. This protective coating filminhibits the solvent from subsequently undergoing an oxidation reaction.The performance deterioration of, in particular, high-voltage batteriescan hence be mitigated. However, there are cases where these compoundsare reduced at the negative electrode to form a high-resistance coatingfilm and this adversely influences battery characteristics includinghigh-load characteristics. When at least one compound selected from thegroup consisting of unsaturated carbonates, fluorine-containingcarbonates, monofluorophosphates, and difluorophosphates coexists in theelectrolyte, these compounds are reduced at the negative electrode at anobler potential than the polyamine compound and/or polyamide compoundto form a protective coating film and thereby inhibit the polyaminecompound and/or polyamide compound from reacting at the negativeelectrode. As a result, no high-resistance coating film is formed on thenegative electrode, and a stable coating film is formed on the positiveelectrode to inhibit the electrolyte from reacting with the positiveelectrode. Consequently, the continuous-charge characteristics of thenonaqueous-electrolyte secondary battery can be greatly heightened.

[4. Nonaqueous Organic Solvent]

The nonaqueous organic solvent is not particularly limited, and knownnonaqueous organic solvents can be used at will so long as theelectrolyte which will be described later can dissolve therein. Examplesthereof include acyclic carbonates, cyclic carbonates, acyclic esters,cyclic esters (lactone compounds), acyclic ethers, cyclic ethers, andsulfur-containing organic solvents. Preferred of these are acycliccarbonates, cyclic carbonates, acyclic esters, cyclic esters, acyclicethers, or cyclic ethers as solvents having high ionic conductivity.These solvents are the same as those described above with regard tononaqueous electrolytes 1 to 4. However, the following are preferred.

Examples of the acyclic carbonates include dimethyl carbonate, diethylcarbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethylpropyl carbonate.

Examples of the cyclic carbonates include ethylene carbonate, propylenecarbonate, butylene carbonate, fluoroethylene carbonate,difluoroethylene carbonate, fluoropropylene carbonate, andtrifluoromethylethylene carbonate.

Examples of the acyclic ethers include 1,2-dimethoxyethane,1,2-diethoxyethane, and diethyl ether.

Examples of the cyclic ethers include tetrahydrofuran,2-methyltetrahydrofuran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane.

Examples of the acyclic esters include methyl formate, methyl acetate,and methyl propionate.

Examples of the cyclic esters include γ-butyrolactone andγ-valerolactone.

One nonaqueous organic solvent may be used alone, or any desiredcombination of two or more nonaqueous organic solvents in any desiredproportion may be used. However, it is preferred to use a mixture of twoor more nonaqueous organic solvents in order to impart the desiredcharacteristics, i.e., continuous-charge characteristics. In particular,it is preferred that the mixture should consist mainly of at least onecyclic carbonate and (at least one acyclic carbonate or at least onecyclic ester). The term “consist mainly of” as used here means that thenonaqueous organic solvents include at least one cyclic carbonate and(at least one acyclic carbonate or at least one cyclic ester) in a totalamount of 70% by mass or larger based on the whole nonaqueouselectrolyte.

In the case where two or more nonaqueous organic solvents are used incombination, examples of preferred combinations include: binary solventssuch as ethylene carbonate/methyl ethyl carbonate, ethylenecarbonate/diethyl carbonate, and ethylene carbonate/γ-butyrolactone; andternary solvents such as ethylene carbonate/dimethyl carbonate/ethylmethyl carbonate and ethylene carbonate/methyl ethyl carbonate/diethylcarbonate. Nonaqueous organic solvents mainly including these compoundsare suitable because they attain a satisfactory balance among variousproperties.

In the case where an organic solvent is used as the nonaqueous organicsolvent, the number of carbon atoms of the organic solvent is generally3 or larger and is generally 13 or smaller, preferably 7 or smaller.When the number of carbon atoms thereof is too large, there are caseswhere this organic solvent shows poor infiltration into the separatorand negative electrode, making it impossible to attain sufficientcapacity. On the other hand, when the number of carbon atoms thereof istoo small, there are cases where this organic solvent has enhancedvolatility to form a cause of an increase in the internal pressure ofthe battery.

The molecular weight of the nonaqueous organic solvent is generally 50or higher, preferably 80 or higher, and is generally 250 or lower,preferably 150 or lower. When the molecular weight thereof is too high,there are cases where this nonaqueous organic solvent shows poorinfiltration into the separator and negative electrode, making itimpossible to attain sufficient capacity. On the other hand, when themolecular weight thereof is too low, there are cases where thisnonaqueous organic solvent has enhanced volatility to form a cause of anincrease in the internal pressure of the battery.

Furthermore, in the case where two or more nonaqueous organic solventsare used in combination, the proportion of a cyclic carbonate in thenonaqueous organic solvents is generally 5% by mass or higher,preferably 10% by mass or higher, more preferably 15% by mass or higher,especially preferably 20% by mass or higher, and is generally 60% bymass or lower, preferably 50% by mass or lower, especially preferably40% by mass or lower, based on the whole nonaqueous organic solvents.When the proportion thereof is lower than the lower limit of that range,lithium salt dissociation is less apt to occur and electricalconductivity decreases. Consequently, high-load capacity is apt todecrease. On the other hand, when the proportion thereof exceeds theupper limit, this electrolyte has too high a viscosity and lithium ionsare less apt to move. There are hence cases where high-load capacitydecreases.

[5. Lithium Salt]

The lithium salt to be used as an electrolyte may be any of inorganiclithium salts and organic lithium salts. Examples thereof include thesame “lithium salts” as those enumerated above under “Electrolyte” withregard to nonaqueous electrolyte 1. Examples of the inorganic lithiumsalts include: inorganic fluoride salts such as LiPF₆, LiAsF₆, LiBF₄,and LiSbF₆; inorganic chloride salts such as LiAlCl₄; and perhalogenacid salts such as LiClO₄, LiBrO₄, and LiIO₄. Examples of the organiclithium salts include fluorine-containing organic lithium salts such as:perfluoroalkanesulfonic acid salts, e.g., CF₃SO₃Li and C₄F₉SO₃Li;perfluoroalkanecarboxylic acid salts, e.g., CF₃COOLi;perfluoroalkanecarbonimide salts, e.g., (CF₃CO)₂NLi; andperfluoroalkanesulfonimide salts, e.g., (CF₃SO₂)₂NLi and (C₂F₅SO₂)₂NLi,and the like.

Of these, LiPF₆, LiBF₄, CF₃SO₃Li, (CF₃SO₂)₂NLi, and the like arepreferred because these salts are apt to dissolve in solvents and have ahigh degree of dissociation. One electrolyte may be used alone, or anydesired combination of two or more electrolytes in any desiredproportion may be used. In particular, a combination of LiPF₅ and LiBF₄or a combination of LiPF₆ and (CF₃SO₂)₂NLi is preferred because thesecombinations are effective in improving continuous-chargecharacteristics.

The concentration of the electrolyte in the nonaqueous electrolyte isgenerally 0.5 mol/L or higher, preferably 0.75 mol/L or higher, and isgenerally 2 mol/L or lower, preferably 1.75 mol/L or lower, based on thenonaqueous electrolyte. When the concentration thereof is too low, thereare cases where this nonaqueous electrolyte has an insufficientelectrical conductivity. On the other hand, in case where theconcentration thereof is too high, this nonaqueous electrolyte has anincreased viscosity and, hence, a reduced electrical conductivity and isapt to suffer deposition at low temperatures. There is hence a tendencythat the nonaqueous-electrolyte secondary battery has reducedperformances.

[6. Other Aids]

“Other aids” may be incorporated into nonaqueous electrolyte 5 of theinvention for the purpose of improving the wetting properties of thenonaqueous electrolyte, overcharge characteristics, etc., unless theeffects of invention 5 are lessened thereby. Examples of the “otheraids” include: acid anhydrides such as maleic anhydride, succinicanhydride, and glutaric anhydride; carboxylic acid esters such as vinylacetate, divinyl adipate, and allyl acetate; sulfur-containing compoundssuch as diphenyl disulfide, 1,3-propanesultone, 1,4-butanesultone,dimethyl sulfone, divinyl sulfone, dimethyl sulfite, ethylene sulfite,1,4-butanediol dimethanesulfonate, methyl methanesulfonate, and2-propynyl methanesulfonate; and aromatic compounds such ast-butylbenzene, biphenyl, o-terphenyl, 4-fluorobiphenyl, fluorobenzene,2,4-difluorobenzene, cyclohexylbenzene, diphenyl ether,2,4-difluoroanisole, and trifluoromethylbenzene and these aromaticcompounds substituted with a fluorine atom. One of such “other aids” maybe used alone, or any desired combination of two or more thereof in anydesired proportion may be used.

The concentration of the “other aids” in the nonaqueous electrolyte isgenerally 0.01% by mass or higher, preferably 0.05% by mass or higher,and is generally 10% by mass or lower, preferably 5% by mass or lower,based on the whole nonaqueous electrolyte. In the case of using two ormore of the “other aids” in combination, these ingredients are used sothat the total concentration thereof is within the range shown above.

[7. State of Nonaqueous Electrolyte]

Nonaqueous electrolyte 5 is present usually in a liquid state. However,this electrolyte may be caused to gel with a polymer to obtain asemi-solid electrolyte. For the gelation, any desired polymer may beused. Examples of the polymer include poly(vinylidene fluoride),copolymers of poly(vinylidene fluoride) and hexafluoropropylene,poly(ethylene oxide), polyacrylates, and polymethacrylates. One polymermay be used alone for the gelation, or any desired combination of two ormore polymers in any desired proportion may be used for the gelation.

In the case where nonaqueous electrolyte 5 is used in the form of asemi-solid electrolyte, the proportion of the nonaqueous electrolyte tothe semi-solid electrolyte is generally 30% by mass or higher,preferably 50% by mass or higher, especially preferably 75% by mass orhigher, and is generally 99.95% by mass or lower, preferably 99% by massor lower, especially preferably 98% by mass or lower, based on the totalamount of the semi-solid electrolyte. When the proportion of thenonaqueous electrolyte is too high, there are cases where it isdifficult to retain the electrolyte and liquid leakage is apt to occur.Conversely, when the proportion thereof is too low, there are caseswhere this electrolyte is insufficient in charge/discharge efficiencyand capacity.

[8. Process for Producing Nonaqueous Electrolyte]

Nonaqueous electrolyte 5 of the invention can be prepared by dissolvinga lithium salt, the cyclic polyamine compound and/or cyclic polyamidecompound according to invention 5, and “at least one compound selectedfrom the group consisting of unsaturated carbonates, fluorine-containingcarbonates, monofluorophosphates, and difluorophosphates” in anonaqueous organic solvent optionally together with “other aids”.

It is preferred that in preparing nonaqueous electrolyte 5, each of theraw materials for the nonaqueous electrolyte, i.e., the lithium salt,cyclic polyamine compound and/or cyclic polyamide compound according toinvention 5, nonaqueous organic solvent, and “other aids”, should bedehydrated beforehand. With respect to the degree of dehydration, it isdesirable to dehydrate each raw material to generally 50 ppm or lower,preferably 30 ppm or lower. In this description, ppm means proportion byweight.

When water is present in the nonaqueous electrolyte, there are caseswhere electrolysis of the water, reaction of the water with lithiummetal, hydrolysis of the lithium salt, etc. occur. Techniques for thedehydration are not particularly limited. However, in the case where thematerial to be dehydrated is, for example, a liquid, e.g., a nonaqueousorganic solvent, a molecular sieve or the like may be used. In the casewhere the material to be dehydrated is a solid, e.g., a lithium salt,this material may be dried at a temperature lower than decompositiontemperatures.

Embodiment 5-2

Another essential point of invention 5 resides in a nonaqueouselectrolyte which includes a nonaqueous organic solvent and a lithiumsalt dissolved therein, and is characterized in that the nonaqueousorganic solvent contains a cyclic polyamine compound and furthercontains at least one cyclic carbonate in an amount of from 5% by massto 40% by mass based on the whole nonaqueous organic solvent. Thiselectrolyte is referred to as “embodiment 5-2”.

[1. Cyclic Polyamine Compound]

[1-1. Kind]

The kind of the cyclic polyamine compound is as described above.

[1-2. Composition]

The composition is as described above.

[2. Cyclic Carbonate]

The cyclic carbonate in invention 5 is not particularly limited so longas it is a cyclic carbonate. Part or all of the hydrogen atoms may havebeen replaced with a halogen, e.g., fluorine or chlorine. Examplesthereof include ethylene carbonate, propylene carbonate, butylenecarbonate, fluoroethylene carbonate, difluoroethylene carbonate,fluoropropylene carbonate, and trifluoromethylethylene carbonate. One ofsuch cyclic carbonates may be used alone, or any desired combination oftwo or more there in any desired proportion may be used.

Especially preferred are: a combination of ethylene carbonate andpropylene carbonate; a combination of ethylene carbonate andfluoroethylene carbonate; and a combination of ethylene carbonate,propylene carbonate, and fluoroethylene carbonate.

Invention 5 is characterized in that the nonaqueous organic solventcontains a cyclic carbonate in an amount of 5-40% by mass based on thewhole nonaqueous organic solvent. The lower limit of the content thereofis preferably 8% by mass or higher, especially preferably 10% by mass orhigher, more preferably 12% by mass or higher. The upper limit thereofis preferably 35% by mass or lower, especially preferably 30% by mass orlower, more preferably 25% by mass or lower. Two or more cycliccarbonates may be used in combination so long as the total amountthereof is within the range shown above.

In case where the proportion of the cyclic carbonate is lower than thelower limit of that range, lithium salt dissociation is apt to occur andelectrical conductivity hence decreases. Consequently, high-loadcapacity is apt to decrease. In case where the proportion thereofexceeds the upper limit, the nonaqueous organic solvent including thecyclic carbonate comes to undergo a decomposition reaction catalyzed bythe polyamine compound. There are hence cases where a gas, e.g., carbondioxide, generates in a large amount during high-temperature continuouscharge, resulting in an increase in resistance and a decrease inrecovery capacity.

The number of carbon atoms of the cyclic carbonate is generally 3 orlarger and is generally 13 or smaller, preferably 5 or smaller. When thenumber of carbon atoms thereof is too large, there are cases where thiscyclic carbonate shows poor infiltration into the separator and negativeelectrode, making it impossible to attain sufficient capacity. On theother hand, when the number of carbon atoms thereof is too small, thereare cases where this cyclic carbonate has enhanced volatility to form acause of an increase in the internal pressure of the battery.

[3. Nonaqueous Organic Solvent]

The nonaqueous organic solvent is as described above.

[4. Lithium Salt]

The lithium salt is as described above.

[5. At Least One Compound Selected from Group Consisting of UnsaturatedCarbonates, Fluorine-Containing Carbonates, Monofluorophosphates, andDifluorophosphates]

In embodiment 5-2 also, it is preferred to incorporate at least onecompound selected from the group consisting of unsaturated carbonates,fluorine-containing carbonates, monofluorophosphates, anddifluorophosphates. These compounds are as described above.

[6. Other Aids]

Other aids are as described above.

[7. State of Nonaqueous Electrolyte]

The state of the nonaqueous electrolyte is as described above.

[8. Process for Producing Nonaqueous Electrolyte]

The process is as described above.

Embodiment 5-3

Still another essential point of invention 5 resides in a nonaqueouselectrolyte which includes a nonaqueous organic solvent and a lithiumsalt dissolved therein, and is characterized by containing a cyclicpolyamide compound. This electrolyte is referred to as “embodiment 5-3”.

[1. Cyclic Polyamide Compound]

[1-1. Kind]

The kind of the cyclic polyamide compound is as described above.

[1-2. Composition]

The composition is as described above.

[2. Nonaqueous Organic Solvent]

Usable nonaqueous solvents are as described above.

The reason why a cyclic polyamide compound, even when used alone,enables the effects of this invention to be produced is as follows. In acyclic polyamide compound, the unshared electron pairs on the respectivenitrogen atoms are in a delocalized state due to the influence of theadjoining carbonyl groups. Cyclic polyamide compounds hence have farlower basicity than cyclic polyamine compounds. Because of this, evenwhen a solvent such as a cyclic carbonate is used in a large amount,this solvent is less apt to react on the negative electrode.Consequently, the kinds of the solvents to be used and the compositionthereof are not particularly limited.

[3. Lithium Salt]

The lithium salt is as described above.

[4. Cyclic Carbonate]

In embodiment 5-3 also, it is preferred to incorporate a cycliccarbonate. The cyclic carbonate is as described above.

[5. At Least One Compound Selected from Group Consisting of UnsaturatedCarbonates, Fluorine-Containing Carbonates, Monofluorophosphates, andDifluorophosphates]

In embodiment 5-3 also, it is preferred to incorporate at least onecompound selected from the group consisting of unsaturated carbonates,fluorine-containing carbonates, monofluorophosphates, anddifluorophosphates. These compounds are as described above.

[6. Other Aids]

Other aids are as described above.

[7. State of Nonaqueous Electrolyte]

The state of the nonaqueous electrolyte is as described above.

[8. Process for Producing Nonaqueous Electrolyte]

The process is as described above.

II. Nonaqueous-Electrolyte Secondary Battery

Nonaqueous-electrolyte secondary battery 5 of the invention includes: anegative electrode and a positive electrode which are capable ofoccluding/releasing ions; and the nonaqueous electrolyte of thisinvention.

<2-1. Battery Constitution>

Nonaqueous-electrolyte secondary battery 5 of the invention may have thesame battery constitution as that described above with regard tononaqueous-electrolyte secondary battery 1.

<2-2. Nonaqueous Electrolyte>

As the nonaqueous electrolyte, the nonaqueous electrolyte 5 of theinvention described above is used. Incidentally, a mixture of nonaqueouselectrolyte 5 of the invention and another nonaqueous electrolyte may beused so long as this is not counter to the spirit of invention 5.

<2-3. Negative Electrode>

The negative electrode of nonaqueous-electrolyte secondary battery 5 maybe the same as the negative electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-4. Positive Electrode>

The positive electrode of nonaqueous-electrolyte secondary battery 5 maybe the same as the positive electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-5. Separator>

The separator of nonaqueous-electrolyte secondary battery 5 may be thesame as the separator described above with regard tononaqueous-electrolyte secondary battery 1.

<2-6. Battery Design>

The battery design of nonaqueous-electrolyte secondary battery 5 may bethe same as the battery design described above with regard tononaqueous-electrolyte secondary battery 1.

[1. Nonaqueous Electrolyte 6]

Like ordinary nonaqueous electrolytes, nonaqueous electrolyte 6 of theinvention includes an electrolyte and a nonaqueous solvent containingthe electrolyte dissolved therein.

<1-1. Electrolyte>

The electrolyte to be used in nonaqueous electrolyte 6 of the inventionis not limited, and known ones for use as electrolytes in a targetnonaqueous-electrolyte secondary battery can be employed and mixed atwill. In the case where nonaqueous electrolyte 6 of the invention is tobe used in a nonaqueous-electrolyte secondary battery, the electrolytepreferably is one or more lithium salts. The electrolyte in nonaqueouselectrolyte 6 may be the same as that described above with regard tononaqueous electrolyte 1.

Nonaqueous electrolyte 6 of the invention includes a nonaqueous solventand an electrolyte dissolved therein, and this nonaqueous electrolyte 6contains “at least one cyclic disulfonylimide salt represented bygeneral formula (8)” and “a monofluorophosphate and/or adifluorophosphate”.

[In the formula, R represents an alkylene group which has 1-12 carbonatoms and may be substituted with an alkyl group, provided that thealkyl group(s) and the alkylene group may be substituted with a fluorineatom; n is an integer of 1 to 3; and M is one or more metals selectedfrom Group 1, Group 2, and Group 13 of the periodic table or aquaternary onium.]<1-2. Cyclic Disulfonylimide Salt Represented by General Formula (8)>

In the cyclic disulfonylimide salt represented by general formula (8), Rrepresents an alkylene group which has 1-12, preferably 2-8 carbon atomsand which may be substituted with an alkyl group. The alkyl groups andthe alkylene group may have been further substituted with a fluorineatom. When the number of carbon atoms thereof is too large, thisdisulfonylimide salt has an increased molecular weight per molecule andthere are hence cases where the expected effect is lessened.

Examples of the unsubstituted alkylene group having 1-12 carbon atomsinclude ethylene, trimethylene, tetramethylene, and pentamethylene.Examples of the alkyl groups which may be introduced as substituentsinclude linear or branched alkyl groups having preferably 1-8,especially preferably 1-4 carbon atoms. These groups may have beenfurther substituted with a fluorine atom. Examples of the alkylene groupsubstituted with an alkyl group include propylene, 2-methyltrimethylene,and neopentylene.

Any desired number of fluorine atoms can be introduced into any desiredsites in such an unsubstituted alkylene group or alkyl-substitutedalkylene group. Of such fluorinated alkylene groups, perfluoroalkylenegroups are preferred from the standpoints of industrial availability,ease of production, etc. For example, perfluoroethylene andperfluorotrimethylene are especially preferred.

In the cyclic disulfonylimide salt represented by general formula (8), Mis one or more metals selected from Group 1, Group 2, and Group 13 ofthe periodic table (hereinafter sometimes referred to as “specificmetals”) or a quaternary onium.

Examples of the metals in Group 1 of the periodic table include lithium,sodium, potassium, and cesium. Preferred of these are lithium andsodium. Especially preferred is lithium.

Examples of the metals in Group 2 of the periodic table includemagnesium, calcium, strontium, and barium. Preferred of these aremagnesium and calcium. Especially preferred is magnesium.

Examples of the metals in Group 13 of the periodic table includealuminum, gallium, indium, and thallium. Preferred of these are aluminumand gallium. Especially preferred is aluminum.

Preferred of these specific metals is lithium, sodium, magnesium,calcium, aluminum, or gallium. More preferred is lithium, magnesium, oraluminum. Lithium is especially preferred.

One or more of such cyclic disulfonylimide salts represented by generalformula (8) may be used. It is also possible for the salt to have two ormore kinds of cyclic disulfonylimide anions together with the M^(n+)common to these. Namely, it is possible for the salt to have two or morekinds of cyclic disulfonylimide anions in the molecule.

Examples of the cyclic disulfonylimide salt represented by generalformula (8) include

the lithium salt of cyclic 1,2-ethanedisulfonylimide, lithium salt ofcyclic 1,3-propanedisulfonylimide, lithium salt of cyclic1,2-perfluoroethanedisulfonylimide, lithium salt of cyclic1,3-perfluoropropanedisulfonylimide, and lithium salt of cyclic1,4-perfluorobutanedisulfonylimide, and the like.

Preferred of these are the lithium salt of cyclic1,2-perfluoroethanedisulfonylimide and the lithium salt of cyclic1,3-perfluoropropanedisulfonylimide.

The concentration of the cyclic disulfonylimide salt represented bygeneral formula (8) in the nonaqueous electrolyte is preferably 0.001-1mol/L. When the concentration of the cyclic disulfonylimide salt is toolow, there are cases where it is difficult to sufficiently inhibit gasevolution during high-temperature storage or capacity deteriorationthrough high-temperature storage. Conversely, too high concentrationsthereof may result in cases where battery characteristics decreasethrough high-temperature storage. The concentration of the cyclicdisulfonylimide salt is more preferably 0.01 mol/L or higher, especiallypreferably 0.02 mol/L or higher, more preferably 0.03 mol/L or higher.The upper limit thereof is preferably 0.5 mol/L or lower, morepreferably 0.3 mol/L or lower, especially preferably 0.2 mol/L or lower.

<1-3. Nonaqueous Solvent>

The nonaqueous solvent contained in nonaqueous electrolyte 6 of theinvention is not particularly limited so long as it is a solvent whichdoes not adversely influence battery characteristics after batteryfabrication. However, it is preferred to employ one or more of thefollowing solvents for use in nonaqueous electrolytes.

Examples of nonaqueous solvents in ordinary use include acyclic andcyclic carbonates, acyclic and cyclic carboxylic acid esters, acyclicand cyclic ethers, phosphorus-containing organic solvents, andsulfur-containing organic solvents. These solvents are the same as thosedescribed above with regard to nonaqueous electrolytes 1 to 5.

<1-4. Monofluorophosphate and Difluorophosphate>

With respect to the “monofluorophosphate and difluorophosphate” to beused in invention 6, the kinds and contents thereof, places where thesalts exist, methods of analysis, production process, etc. are the sameas those described above with regard to nonaqueous electrolyte 1.

<1-5. Additives>

Nonaqueous electrolyte 6 of the invention may contain various additivesso long as these additives do not considerably lessen the effects ofinvention 6. In the case where additives are additionally incorporatedto prepare the nonaqueous electrolyte, conventionally known additivescan be used at will. One additive may be used alone, or any desiredcombination of two or more additives in any desired proportion may beused.

Examples of the additives include overcharge inhibitors and aids forimproving capacity retentivity after high-temperature storage and cyclecharacteristics. It is preferred to add a carbonate having at leasteither of an unsaturated bond and a halogen atom (hereinafter sometimesreferred to as “specific carbonate”) as an aid for improving capacityretentivity after high-temperature storage and cycle characteristics,among those additives. The specific carbonate and other additives areseparately explained below.

<1-5-1. Specific Carbonate>

The specific carbonate is a carbonate having at least either of anunsaturated bond and a halogen atom. The specific carbonate may have anunsaturated bond only or have a halogen atom only, or may have both anunsaturated bond and a halogen atom.

The molecular weight of the specific carbonate is not particularlylimited, and may be any desired value unless this considerably lessensthe effects of invention 6. However, the molecular weight thereof isgenerally 50 or higher, preferably 80 or higher, and is generally 250 orlower, preferably 150 or lower. When the molecular weight thereof is toohigh, this specific carbonate has reduced solubility in the nonaqueouselectrolyte and there are cases where the effect of the carbonate isdifficult to produce sufficiently.

Processes for producing the specific carbonate also are not particularlylimited, and a known process selected at will can be used to produce thecarbonate.

Any one specific carbonate may be incorporated alone into nonaqueouselectrolyte 6 of the invention, or any desired combination of two ormore specific carbonates in any desired proportion may be incorporatedthereinto.

The amount of the specific carbonate to be incorporated into nonaqueouselectrolyte 6 of the invention is not limited, and may be any desiredvalue unless this considerably lessens the effects of invention 6. Itis, however, desirable that the specific carbonate should beincorporated in a concentration which is generally 0.01% by mass orhigher, preferably 0.1% by mass or higher, more preferably 0.3% by massor higher, and is generally 70% by mass or lower, preferably 50% by massor lower, more preferably 40% by mass or lower, based on nonaqueouselectrolyte 6 of the invention.

When the amount of the specific carbonate is below the lower limit ofthat range, there are cases where use of this nonaqueous electrolyte 6of the invention in a nonaqueous-electrolyte secondary battery resultsin difficulties in producing the effect of sufficiently improving thecycle characteristics of the nonaqueous-electrolyte secondary battery.On the other hand, when the proportion of the specific carbonate is toohigh, there is a tendency that use of this nonaqueous electrolyte 6 ofthe invention in a nonaqueous-electrolyte secondary battery results indecreases in the high-temperature storability and continuous-chargecharacteristics of the nonaqueous-electrolyte secondary battery. Inparticular, there are cases where gas evolution is enhanced and capacityretentivity decreases.

(1-5-1-1. Unsaturated Carbonate)

The carbonate having an unsaturated bond (hereinafter often referred toas “unsaturated carbonate”) as one form of the specific carbonateaccording to invention 6 is the same as that described above with regardto nonaqueous electrolyte 1.

(1-5-1-2. Halogenated Carbonate)

On the other hand, the carbonate having a halogen atom (hereinafteroften referred to as “halogenated carbonate”) as another form of thespecific carbonate according to invention 6 is not particularly limitedso long as it is a carbonate having a halogen atom, and any desiredhalogenated carbonate can be used. This “halogenated carbonate” is thesame as that described above with regard to nonaqueous electrolyte 2.

(1-5-1-3. Halogenated Unsaturated Carbonate)

Furthermore usable as the specific carbonate is a carbonate having bothan unsaturated bond and a halogen atom (this carbonate is suitablyreferred to as “halogenated unsaturated carbonate”). This halogenatedunsaturated carbonate is not particularly limited, and any desiredhalogenated unsaturated carbonate can be used unless the effects ofinvention 6 are considerably lessened thereby. This “halogenatedunsaturated carbonate” is the same as that described above with regardto nonaqueous electrolyte 2.

<1-5-2. Other Additives>

Additives other than the specific carbonate are explained below.Examples of additives other than the specific carbonate includeovercharge inhibitors and aids for improving capacity retentivity afterhigh-temperature storage and cycle characteristics.

<1-5-2-1. Overcharge Inhibitor>

The “overcharge inhibitor” is the same as that described above withregard to nonaqueous electrolyte 1.

<1-5-2-2. Aids>

On the other hand, examples of the aids for improving capacityretentivity after high-temperature storage and cycle characteristicsinclude the same compounds as those enumerated above with regard tononaqueous electrolyte 1.

[2. Nonaqueous-Electrolyte Secondary Battery]

Nonaqueous-electrolyte secondary battery 6 of the invention includes: anegative electrode and a positive electrode which are capable ofoccluding and releasing ions; and the nonaqueous electrolyte 6 of theinvention.

<2-1. Battery Constitution>

Nonaqueous-electrolyte secondary battery 6 of the invention may have thesame battery constitution as that described above with regard tononaqueous-electrolyte secondary battery 1.

<2-2. Nonaqueous Electrolyte>

As the nonaqueous electrolyte, the nonaqueous electrolyte 6 of theinvention described above is used. Incidentally, a mixture of nonaqueouselectrolyte 6 of the invention and another nonaqueous electrolyte may beused so long as this is not counter to the spirit of invention 6.

<2-3. Negative Electrode>

The negative electrode of nonaqueous-electrolyte secondary battery 6 maybe the same as the negative electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-4. Positive Electrode>

The positive electrode of nonaqueous-electrolyte secondary battery 6 maybe the same as the positive electrode described above with regard tononaqueous-electrolyte secondary battery 1.

<2-5. Separator>

The separator of nonaqueous-electrolyte secondary battery 6 may be thesame as the separator described above with regard tononaqueous-electrolyte secondary battery 1.

<2-6. Battery Design>

The battery design of nonaqueous-electrolyte secondary battery 6 may bethe same as the battery design described above with regard tononaqueous-electrolyte secondary battery 1.

EXAMPLES

The invention will be explained below in more detail by reference toExamples and Comparative Examples. However, the invention should not beconstrued as being limited to the following Examples unless theinvention departs from the spirit thereof.

Example 1 of Nonaqueous Electrolyte 1 Production ofNonaqueous-Electrolyte Secondary Battery, 1

[Production of Positive Electrode]

Eighty-five parts by weight of LiCoO₂ (“C5”, manufactured by NipponChemical Industrial Co., Ltd.) was used as a positive-electrode activematerial and mixed with 6 parts by weight of a carbon black and 9 partsby weight of poly(vinylidene fluoride) (trade name “KF-1000”,manufactured by Kureha Chemical Industry Co., Ltd.).N-Methyl-2-pyrrolidone was added to the mixture to slurry it. Thisslurry was evenly applied to each side of an aluminum foil having athickness of 15 μm and dried. Thereafter, the coated foil was pressed soas to result in positive-electrode active-material layers having adensity of 3.0 g/cm³. Thus, a positive electrode was obtained.

[Production of Negative Electrode]

To 98 parts by weight of artificial-graphite powder KS-44 (trade name;manufactured by Timcal) were added 100 parts by weight of an aqueousdispersion of sodium carboxymethyl cellulose (concentration of sodiumcarboxymethyl cellulose, 1% by mass) as a thickener and 2 parts byweight of an aqueous dispersion of a styrene/butadiene rubber(concentration of styrene/butadiene rubber, 50% by mass) as a binder.The ingredients were mixed together by means of a disperser to obtain aslurry. The slurry obtained was applied to one side of a copper foilhaving a thickness of 12 μm and dried. Thereafter, the coated foil waspressed so as to result in a negative-electrode active-material layerhaving a density of 1.5 g/cm³. Thus, a negative electrode was obtained.

[Nonaqueous Electrolyte]

In a dry argon atmosphere, LiPF₆ which each had been sufficiently driedwas dissolved, in an amount of 1 mol/L, in a nonaqueous solvent preparedby mixing in the proportion shown in Table 1. Thus, a nonaqueouselectrolyte was prepared. Furthermore, a monofluorophosphate and/or adifluorophosphate was dissolved in the solution so as to result in therespective concentrations shown in Table 1. Thus, a desired nonaqueouselectrolyte was obtained.

[Fabrication of Nonaqueous-Electrolyte Secondary Battery]

The positive electrode and negative electrode described above and aseparator made of polyethylene were superposed in the order of negativeelectrode/separator/positive electrode/separator/negative electrode toproduce a battery element. This battery element was inserted into a bagconstituted of a laminated film obtained by coating both sides ofaluminum (thickness, 40 μm) with a resin layer, with terminals of thepositive and negative electrodes projecting outward. Thereafter, 0.5 mLof the nonaqueous electrolyte was introduced into the bag, and this bagwas vacuum-sealed to produce a sheet battery.

<Evaluation of Nonaqueous-Electrolyte Secondary Battery forHigh-Temperature Storability>

The battery in a sheet form was evaluated in the state of beingsandwiched between glass plates in order to enhance contact between theelectrodes. At 25° C., this battery was subjected to 3 cycles ofcharge/discharge at a constant current corresponding to 0.2 C and at afinal charge voltage of 4.2V and a final discharge voltage of 3V tostabilize the battery. In the fourth cycle, the battery was subjected to4.4V constant-current constant-voltage charge (CCCV charge) (0.05 Ccutting) in which the battery was charged to a final charge voltage of4.4V at a current corresponding to 0.5 C and further charged until thecharge current value reached a current value corresponding to 0.05 C.Thereafter, this battery was subjected to 3V discharge at a constantcurrent corresponding to 0.2 C to determine the discharge capacity ofthe battery before high-temperature storage. This battery was subjectedagain to 4.4V CCCV (0.05 C cutting) charge and then stored at a hightemperature under the conditions of 85° C. and 24 hours.

Before and after the high-temperature storage, the sheet battery wasimmersed in an ethanol bath. The amount of the gas evolved wasdetermined from the resultant volume change. The battery which hadundergone the storage was discharged at 25° C. and a constant current of0.2 C to a final discharge voltage of 3V to obtain the residual capacityafter the storage test. This battery was subjected again to 4.4V CCCV(0.05 C cutting) charge and then discharged to 3V at a current valuecorresponding to 0.2 C to determine the 0.2 C capacity and therebyobtain the 0.2 C capacity of the battery which had undergone the storagetest. This capacity was taken as recovery capacity. “1 C” means acurrent value at which the battery can be fully charged by 1-hourcharge.

The residual capacity and recovery capacity (%) in the case where thedischarge capacity as measured before the high-temperature storage istaken as 100 are shown in Table 1.

Example 2 of Nonaqueous Electrolyte 1 to Example 55 of NonaqueousElectrolyte 1 and Comparative Example 1 for Nonaqueous Electrolyte 1 toComparative Example 12 for Nonaqueous Electrolyte 1

Desired aqueous electrolytes were prepared in the same manner as inExample 1 of Nonaqueous Electrolyte 1, except that the nonaqueoussolvent and the monofluorophosphate and/or difluorophosphate which areshown in Tables 1 to 5 were used so as to result in the contents shownin Tables 1 to 5. Nonaqueous-electrolyte secondary batteries wereproduced and then evaluated for high-temperature storability in the samemanner as in Example 1 of Nonaqueous Electrolyte 1. The results thereofare shown in Table 1 to Table 5.

TABLE 1 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Residual Recovery difluorophosphateswell capacity capacity Nonaqueous solvent (mass %) (mass %) (mL) (%)(%) Example 1 ethylene carbonate + lithium difluorophosphate 0.18 82 89ethyl methyl carbonate + (0.5) fluoroethylene carbonate (35.4:63.6:1.0)Example 2 ethylene carbonate + lithium difluorophosphate 0.14 80 87ethyl methyl carbonate + (0.5) fluoroethylene carbonate (35.7:64.1:0.2)Example 3 ethylene carbonate + lithium difluorophosphate 0.22 83 88ethyl methyl carbonate + (0.5) fluoroethylene carbonate (34.0:61.0:5.0)Example 4 ethylene carbonate + lithium difluorophosphate 0.19 83 88ethyl methyl carbonate + (0.5) 4,5-difluoroethylene carbonate(35.4:63.6:1.0) Example 5 ethylene carbonate + lithium difluorophosphate0.20 82 88 ethyl methyl carbonate + (0.5) 4-fluoro-5-methylethylenecarbonate (35.4:63.6:1.0) Example 6 ethylene carbonate + lithiumdifluorophosphate 0.21 81 86 ethyl methyl carbonate + (0.5)4-(fluoromethyl)ethylene carbonate (35.4:63.6:1.0) Example 7 ethylenecarbonate + lithium difluorophosphate 0.22 83 89 ethyl methylcarbonate + (0.5) 4-(trifluoromethyl)ethylene carbonate (35.4:63.6:1.0)Example 8 ethylene carbonate + lithium difluorophosphate 0.20 82 87ethyl methyl carbonate + (0.5) fluoroethylene carbonate +2,2-difluoroethyl methyl carbonate (35.4:63.6:0.5:0.5) Example 9ethylene carbonate + lithium difluorophosphate 0.22 81 85 ethyl methylcarbonate + (0.1) fluoroethylene carbonate (35.4:63.6:1.0) Example 10ethylene carbonate + lithium difluorophosphate 0.13 81 87 ethyl methylcarbonate + (1.0) fluoroethylene carbonate (35.4:63.6:1.0) Example 11ethylene carbonate + sodium difluorophosphate 0.20 83 87 ethyl methylcarbonate + (0.5) fluoroethylene carbonate (35.4:63.6:1.0) Example 12ethylene carbonate + dilithium monofluoro- 0.21 82 85 ethyl methylcarbonate + phosphate fluoroethylene carbonate (0.5) (35.4:63.6:1.0)Example 13 ethylene carbonate + lithium difluorophosphate 0.23 82 86ethyl methyl carbonate + (0.5) fluoroethylene carbonate + vinylenecarbonate (35.0:63.0:1.0:1.0)

TABLE 2 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Residual Recovery difluorophosphateswell capacity capacity Nonaqueous solvent (wt %) (wt %) (mL) (%) (%)Example 14 fluoroethylene carbonate + Lithium difluorophosphate 0.22 8188 ethyl methyl carbonate (0.5) (38.8:61.2) Example 15 fluoroethylenecarbonate + Lithium difluorophosphate 0.15 82 87 ethyl methyl carbonate(0.5) (20.7:79.3) Example 16 fluoroethylene carbonate + Lithiumdifluorophosphate 0.24 80 89 ethyl methyl carbonate (0.5) (59.6:40.4)Example 17 fluoroethylene carbonate + Lithium difluorophosphate 0.16 8189 ethylene carbonate + (0.5) ethyl methyl carbonate (17.5:19.9:62.6)Example 18 4,5-difluoroethylene carbonate + Lithium difluorophosphate0.22 80 85 ethyl methyl carbonate (0.5) (38.9:61.1) Example 194-fluoro-5-methylethylene carbonate + Lithium difluorophosphate 0.20 8287 ethyl methyl carbonate (0.5) (36.5:63.5) Example 204-(fluoromethyl)ethylene carbonate + Lithium difluorophosphate 0.18 8085 ethyl methyl carbonate (0.5) (36.2:63.8) Example 214-(trifluoromethyl)ethylene carbonate + Lithium difluorophosphate 0.1781 86 ethyl methyl carbonate (0.5) (39.8:60.2) Example 22 fluoroethylenecarbonate + Lithium difluorophosphate 0.24 80 84 ethyl methyl carbonate(0.1) (38.8:61.2) Example 23 fluoroethylene carbonate + Lithiumdifluorophosphate 0.16 81 87 ethyl methyl carbonate (1.0) (38.8:61.2)Example 24 fluoroethylene carbonate + Sodium difluorophosphate 0.20 8087 ethyl methyl carbonate (0.5) (38.8:61.2) Example 25 fluoroethylenecarbonate + Dilithium monofluoro- 0.22 81 86 ethyl methyl carbonatephosphate (38.8:61.2) (0.5) Example 26 fluoroethylene carbonate +Lithium difluorophosphate 0.21 82 87 ethyl methyl carbonate + (0.5)ethyl 2,2-difloroethyl carbonate (38.4:60.6:1.0) Example 27fluoroethylene carbonate + Lithium difluorophosphate 0.19 80 84 ethylmethyl carbonate + (0.5) ethyl (2,2-difloroethyl) carbonate(38.1:51.6:10.3) Example 28 fluoroethylene carbonate + Lithiumdifluorophosphate 0.18 83 86 ethyl methyl carbonate + (0.5)bis(2,2,2-trifloroethyl) carbonate (37.2:50.3:12.5) Example 29fluoroethylene carbonate + Lithium difluorophosphate 0.24 82 88 ethylmethyl carbonate + (0.5) vinylene carbonate (38.4:60.6:1.0)

TABLE 3 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Residual Recovery difluorophosphateswell capacity capacity Nonaqueous solvent (mass %) (mass %) (mL) (%)(%) Example 30 ethylene carbonate + Lithium difluorophosphate 0.23 82 89ethyl methyl carbonate + (0.5) ethyl-(2,2-difluoroethyl) carbonate(35.4:63.6:1.0) Example 31 ethylene carbonate + Lithiumdifluorophosphate 0.20 83 88 ethyl methyl carbonate + (0.5)ethyl-(2,2-difluoroethyl) carbonate (35.7:64.1:0.2) Example 32 ethylenecarbonate + Lithium difluorophosphate 0.24 81 86 ethyl methylcarbonate + (0.5) ethyl-(2,2-difluoroethyl) carbonate (34.0:61.0:5.0)Example 33 ethylene carbonate + Lithium difluorophosphate 0.23 83 88ethyl methyl carbonate + (0.5) ethyl-(2,2,2-trifluoroethyl) carbonate(35.4:63.6:1.0) Example 34 ethylene carbonate + Lithiumdifluorophosphate 0.21 82 88 ethyl methyl carbonate + (0.5)bis(2,2,2-trifluoroethyl) carbonate (35.4:63.6:1.0) Example 35 ethylenecarbonate + Lithium difluorophosphate 0.22 81 88 ethyl methylcarbonate + (0.5) fluoromethyl methyl carbonate (35.4:63.6:1.0) Example36 ethylene carbonate + Lithium difluorophosphate 0.22 82 87 ethylmethyl carbonate + (0.5) bis(monofluoromethyl) carbonate (35.4:63.6:1.0)Example 37 ethylene carbonate + Lithium difluorophosphate 0.25 81 85ethyl methyl carbonate + (0.1) ethyl-(2,2-difluoroethyl) carbonate(35.4:63.6:1.0) Example 38 ethylene carbonate + Lithiumdifluorophosphate 0.16 81 88 ethyl methyl carbonate + (1.0)ethyl-(2,2-difluoroethyl) carbonate (35.4:63.6:1.0) Example 39 ethylenecarbonate + Sodium difluorophosphate 0.24 83 88 ethyl methyl carbonate +(0.5) ethyl-(2,2-difluoroethyl) carbonate (35.4:63.6:1.0) Example 40ethylene carbonate + Dilithium monofluoro- 0.23 82 86 ethyl methylcarbonate + phosphate ethyl-(2,2-difluoroethyl) carbonate (0.5)(35.4:63.6:1.0) Example 41 ethylene carbonate + Lithiumdifluorophosphate 0.25 83 89 ethyl methyl carbonate + (0.5)ethyl-(2,2-difluoroethyl) carbonate + vinylene carbonate(35.0:63.0:1.0:1.0)

TABLE 4 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Residual Recovery difluorophosphateswell capacity capacity Nonaqueous solvent (mass %) (mass %) (mL) (%)(%) Example 42 ethylene carbonate + Lithium difluorophosphate 0.21 80 86ethyl-(2,2-difluoroethyl) carbonate (0.5) (31.8:68.2) Example 43ethylene carbonate + Lithium difluorophosphate 0.22 81 87ethyl-(2,2-difluoroethyl) carbonate (0.5) (16.1:83.9) Example 44ethylene carbonate + Lithium difluorophosphate 0.20 80 85ethyl-(2,2-difluoroethyl) carbonate (0.5) (52.1:47.9) Example 45ethylene carbonate + Lithium difluorophosphate 0.20 80 87 ethyl methylcarbonate + (0.5) ethyl-(2,2-difluoroethyl) carbonate (35.1:54.1:10.8)Example 46 ethylene carbonate + Lithium difluorophosphate 0.22 82 89ethyl methyl carbonate + (0.5) ethyl-(2,2,2-trifluoroethyl) carbonate(35.0:54.0:11.0) Example 47 ethylene carbonate + Lithiumdifluorophosphate 0.22 81 89 ethyl methyl carbonate + (0.5)bis(2,2,2-trifluoroethyl) carbonate (34.2:52.7:13.1) Example 48 ethylenecarbonate + Lithium difluorophosphate 0.19 79 85 ethyl methylcarbonate + (0.5) fluoromethyl methyl carbonate (35.0:54.0:11.0) Example49 ethylene carbonate + Lithium difluorophosphate 0.19 78 85 ethylmethyl carbonate + (0.5) bis(monofluoromethyl) carbonate(34.5:53.2:12.3) Example 50 ethylene carbonate + Lithiumdifluorophosphate 0.24 80 83 ethyl 2,2-difluoroethyl carbonate (0.1)(31.8:68.2) Example 51 ethylene carbonate + Lithium difluorophosphate0.15 79 87 ethyl-(2,2-difluoroethyl) carbonate (1.0) (31.8:68.2) Example52 ethylene carbonate + Sodium difluorophosphate 0.22 82 87ethyl-(2,2-difluoroethyl)carbonate (0.5) (31.8:68.2) Example 53 ethylenecarbonate + Dilithium monofluoro- 0.21 80 84 ethyl-(2,2-difluoroethyl)carbonate phosphate (31.8:68.2) (0.5) Example 54 ethylene carbonate +Lithium difluorophosphate 0.22 81 86 ethyl-(2,2-difluoroethyl)carbonate + (0.5) fluoroethylene carbonate (31.5:67.5:1.0) Example 55ethylene carbonate + Lithium difluorophosphate 0.24 82 87ethyl-(2,2-difluoroethyl) carbonate + (0.5) vinylene carbonate(31.5:67.5:1.0)

TABLE 5 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Recovery difluorophosphate swellResidualcapacity capacity Nonaqueous solvent (mass %) (mass %) (mL) (%)(%) Comparative ethylene carbonate + — 0.27 62 67 Example 1 ethyl methylcarbonate (35.8:64.2) Comparative ethylene carbonate + — 0.35 66 76Example 2 ethyl methyl carbonate + fluoroethylene carbonate(35.4:63.6:1.0) Comparative ethylene carbonate + lithiumdifluorophosphate 0.20 67 78 Example 3 ethyl methyl carbonate (0.5)(35.8:64.2) Comparative ethylene carbonate + — 0.42 67 83 Example 4ethyl methyl carbonate + vinylene carbonate (35.4:63.6:1.0) Comparativeethylene carbonate + — 0.45 68 83 Example 5 ethyl methyl carbonate +fluoroethylene carbonate + vinylene carbonate (35.0:63.0:1.0:1.0)Comparative ethylene carbonate + lithium difluorophosphate 0.39 67 82Example 6 ethyl methyl carbonate + (0.5) vinylene carbonate(35.4:63.6:1.0) Comparative fluoroethylene carbonate + — 0.37 70 80Example 7 ethyl methyl carbonate (38.8:61.2) Comparative fluoroethylenecarbonate + — 0.47 70 84 Example 8 ethyl methyl carbonate + vinylenecarbonate (38.4:60.6:1.0) Comparative ethylene carbonate + — 0.33 67 74Example 9 ethyl methyl carbonate + ethyl difluoroethyl carbonate(35.4:63.6:1.0) Comparative ethylene carbonate + — 0.44 68 83 Example 10ethyl methyl carbonate + ethyl difluoroethyl carbonate + vinylenecarbonate (35.0:63.0:1.0:1.0) Comparative ethylene carbonate + — 0.30 6880 Example 11 ethyl-(2,2-difluoroethyl) carbonate (31.8:68.2)Comparative ethylene carbonate + — 0.45 68 84 Example 12ethyl-(2,2-difluoroethyl) carbonate + vinylene carbonate (31.5:67.5:1.0)

The following is apparent from Table 1 to Table 5. Thenonaqueous-electrolyte secondary batteries 1 produced using thenonaqueous electrolytes 1 of the invention, which contained at least onecarbonate having a halogen atom and further contained amonofluorophosphate and/or a difluorophosphate, were inhibited fromswelling during high-temperature storage and from deteriorating inbattery characteristics represented by residual capacity and recoverycapacity, as compared with the nonaqueous-electrolyte secondarybatteries produced using the nonaqueous electrolytes containing one ofthese compounds (Comparative Example 2 for Nonaqueous Electrolyte 1,Comparative Example 3 for Nonaqueous Electrolyte 1, and ComparativeExamples 5 to 12 for Nonaqueous Electrolyte 1) or using the nonaqueouselectrolytes containing neither of those compounds (Comparative Example1 for Nonaqueous Electrolyte 1 and Comparative Example 4 for NonaqueousElectrolyte 1).

Specifically, the electrolytes produced in Example 1 of NonaqueousElectrolyte 1 to Example 55 of Nonaqueous Electrolyte 1 were effectivein inhibiting swelling during high-temperature storage and in inhibitingdeterioration in battery characteristics, as compared with ComparativeExample 1 for Nonaqueous Electrolyte 1 and Comparative Example 4 forNonaqueous Electrolyte 1. Even when compared with the ComparativeExamples for Nonaqueous Electrolyte 1 in which the electrolytescontained only either of a carbonate having a halogen atom and amonofluorophosphate and/or difluorophosphate, the Examples of NonaqueousElectrolyte 1, in which the electrolytes contained both of thesecompounds, were ascertained to have been improved in both inhibition ofswelling during high-temperature storage and inhibition of deteriorationin battery characteristics (for example, comparison between Example 1 ofNonaqueous Electrolyte 1 and Comparative Example 2 for NonaqueousElectrolyte 1; comparison between Example 1 of Nonaqueous Electrolyte 1to Example 8 of Nonaqueous Electrolyte 1 and Comparative Example 3 forNonaqueous Electrolyte 1; and comparison between Example 13 ofNonaqueous Electrolyte 1 and Comparative Example 5 for NonaqueousElectrolyte 1). The same effect was observed also in the case wherenonaqueous electrolytes contained vinylene carbonate, which is anexample of the specific carbonate.

Example 56 of Nonaqueous Electrolyte 1 to Example 74 of NonaqueousElectrolyte 1 and Comparative Example 13 for Nonaqueous Electrolyte 1 toComparative Example 24 for Nonaqueous Electrolyte 1 Production ofNonaqueous-Electrolyte Secondary Battery, 2

Subsequently, nonaqueous-electrolyte secondary batteries were producedin the same manner as in Example 1 of Nonaqueous Electrolyte 1, exceptthat the negative electrode used in Example 1 of Nonaqueous Electrolyte1 was replaced with the silicon-alloy negative electrode describedbelow, and that the nonaqueous electrolytes to be used were prepared inthe following manner. The compounds shown in each of the rows of theExamples of Nonaqueous Electrolyte 1 and the Comparative Examples forNonaqueous Electrolyte 1 in the column “Nonaqueous solvent” and thecolumn “Monofluorophosphate and/or difluorophosphate” in Table 6 toTable 8 were mixed together in the proportion shown therein.Furthermore, LiPF₆ was dissolved as an electrolyte salt as to result ina concentration of 1 mol/L. Thus, desired nonaqueous electrolytes(nonaqueous electrolytes of Example 56 of Nonaqueous Electrolyte 1 toExample 74 of Nonaqueous Electrolyte 1 and Comparative Example 13 forNonaqueous Electrolyte 1 to Comparative Example 24 for NonaqueousElectrolyte 1) were prepared and used.

[Production of Silicon-Alloy Negative Electrode]

As negative-electrode active materials, use was made of 73.2 parts byweight of silicon and 8.1 part by weight of copper as non-carbonmaterials and 12.2 parts by weight of an artificial-graphite powder(“KS-6”, manufactured by Timcal). Thereto were added 54.2 parts byweight of an N-methylpyrrolidone solution containing 12 parts by weightof poly(vinylidene fluoride) (hereinafter abbreviated to “PVDF”) and 50parts by weight of N-methylpyrrolidine. The ingredients were mixedtogether by means of a disperser to slurry the mixture. The slurryobtained was evenly applied to a copper foil having a thickness of 18 μmas a negative-electrode current collector. This coating was firstallowed to dry naturally and thereafter finally dried at 85° C. for awhole day and night under reduced pressure. The resultant coated foilwas pressed so as to result in an electrode density of about 1.5 g/cm³.Thus, a negative electrode was obtained.

<Evaluation of Nonaqueous-Electrolyte Secondary Battery forHigh-Temperature Storability>

Each of the batteries in a sheet form was evaluated in the state ofbeing sandwiched between glass plates in order to enhance contactbetween the electrodes. At 25° C., this battery was subjected to 3cycles of charge/discharge at a constant current corresponding to 0.2 Cand at a final charge voltage of 4.2V and a final discharge voltage of3V to stabilize the battery. In the fourth cycle, the battery wassubjected to 4.2V constant-current constant-voltage charge (CCCV charge)(0.05 C cutting) in which the battery was charged to a final chargevoltage of 4.2V at a current corresponding to 0.5 C and further chargeduntil the charge current value reached a current value corresponding to0.05 C. Thereafter, this battery was subjected to 3V discharge at aconstant current corresponding to 0.2 C to determine the dischargecapacity of the battery before high-temperature storage. This batterywas subjected again to 4.2V-CCCV (0.05 C cutting) charge and then storedat a high temperature under the conditions of 85° C. and 3 days.

Before and after the high-temperature storage, the sheet battery wasimmersed in an ethanol bath. The amount of the gas evolved wasdetermined from the resultant volume change. The battery which hadundergone the storage was discharged at 25° C. and a constant current of0.2 C to a final discharge voltage of 3V to obtain the residual capacityafter the storage test. This battery was subjected again to 4.2V-CCCV(0.05 C cutting) charge and then discharged to 3V at a current valuecorresponding to 0.2 C to determine the 0.2 C capacity and therebyobtain the 0.2 C capacity of the battery which had undergone the storagetest. This capacity was taken as recovery capacity. “1 C” means acurrent value at which the battery can be fully charged by 1-hourcharge.

The residual capacity and recovery capacity (%) in the case where thedischarge capacity as measured before the high-temperature storage istaken as 100 are shown in Table 6 to Table 8.

TABLE 6 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Residual Recovery difluorophosphateswell capacity capacity Nonaqueous solvent (mass %) (mass %) (mL) (%)(%) Example 56 ethylene carbonate + lithium difluorophosphate 0.25 82 89diethyl carbonate + (0.5) fluoroethylene carbonate (36.3:62.7:1.0)Example 57 ethylene carbonate + lithium difluorophosphate 0.26 84 90diethyl carbonate + (0.5) 4,5-difluoroethylene carbonate (36.3:62.7:1.0)Example 58 ethylene carbonate + lithium difluorophosphate 0.28 83 88diethyl carbonate + (0.5) 4-(trifluoromethyl)ethylene carbonate(36.3:62.7:1.0) Example 59 ethylene carbonate + lithiumdifluorophosphate 0.28 82 87 diethyl carbonate + (0.5) fluoroethylenecarbonate + vinylene carbonate (35.9:62.1:1.0:1.0) Example 60fluoroethylene carbonate + lithium difluorophosphate 0.25 83 91 diethylcarbonate (0.5) (39.7:60.3) Example 61 fluoroethylene carbonate +lithium difluorophosphate 0.22 81 88 ethylene carbonate + (0.5) diethylcarbonate (17.2:20.3:61.8) Example 62 4,5-difluoroethylene carbonate +lithium difluorophosphate 0.25 82 90 diethyl carbonate (0.5) (39.9:60.1)Example 63 4-(trifluoromethyl)ethylene carbonate + lithiumdifluorophosphate 0.20 83 89 diethyl carbonate (0.5) (40.7:59.3) Example64 fluoroethylene carbonate + lithium difluorophosphate 0.27 84 91diethyl carbonate + (0.5) vinylene carbonate (39.7:59.3:1)

TABLE 7 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Residual Recovery difluorophosphateswell capacity capacity Nonaqueous solvent (mass %) (mass %) (mL) (%)(%) Example 65 ethylene carbonate + lithium difluorophosphate 0.27 81 89diethyl carbonate + (0.5) ethyl-(2,2-difluoroethyl) carbonate(36.3:62.7:1.0) Example 66 ethylene carbonate + lithiumdifluorophosphate 0.27 82 89 diethyl carbonate + (0.5)ethyl-(2,2,2-trifluoroethyl) carbonate (36.3:62.7:1.0) Example 67ethylene carbonate + lithium difluorophosphate 0.25 83 88 diethylcarbonate + (0.5) bis(2,2,2-trifluoroethyl) carbonate (36.3:62.7:1.0)Example 68 ethylene carbonate + lithium difluorophosphate 0.28 82 90diethyl carbonate + (0.5) ethyl-(2,2-difluoroethyl) carbonate + vinylenecarbonate (35.9:62.1:1.0:1.0) Example 69 ethylene carbonate + lithiumdifluorophosphate 0.25 82 88 ethyl-(2,2-difluoroethyl) carbonate (0.5)(31.8:68.2) Example 70 ethylene carbonate + lithium difluorophosphate0.24 81 86 diethyl carbonate + (0.5) ethyl-(2,2-difluoroethyl) carbonate(35.9:53.1:11.0) Example 71 ethylene carbonate + lithiumdifluorophosphate 0.26 83 88 diethyl carbonate + (0.5)ethyl-(2,2,2-trifluoroethyl) carbonate (35.8:53.0:11.3) Example 72ethylene carbonate + lithium difluorophosphate 0.26 83 88 diethylcarbonate + (0.5) bis(2,2,2-trifluoroethyl) carbonate (34.9:51.7:13.4)Example 73 ethylene carbonate + lithium difluorophosphate 0.25 83 88ethyl-(2,2-difluoroethyl) carbonate + (0.5) fluoroethylene carbonate(31.5:67.5:1.0) Example 74 ethylene carbonate + lithiumdifluorophosphate 0.28 83 89 ethyl-(2,2-difluoroethyl) carbonate + (0.5)vinylene carbonate (31.5:67.5:1.0)

TABLE 8 Results of evaluation of high- temperature storabilityMonofluorophosphate and/or Storage Residual Recovery difluorophosphateswell capacity capacity Nonaqueous solvent (mass %) (mass %) (mL) (%)(%) Comparative ethylene carbonate + — 0.31 60 69 Example 13 diethylcarbonate (36.6:63.4) Comparative ethylene carbonate + — 0.38 68 78Example 14 diethyl carbonate + fluoroethylene carbonate (36.3:62.7:1.0)Comparative ethylene carbonate + lithium difluorophosphate 0.24 64 78Example 15 diethyl carbonate (0.5) (36.6:63.4) Comparative ethylenecarbonate + — 0.45 67 82 Example 16 diethyl carbonate + vinylenecarbonate (36.3:62.7:1.0) Comparative ethylene carbonate + — 0.49 70 83Example 17 diethyl carbonate + fluoroethylene carbonate + vinylenecarbonate (35.9:62.1:1.0:1.0) Comparative ethylene carbonate + lithiumdifluorophosphate 0.38 68 82 Example 18 diethyl carbonate + (0.5)vinylene carbonate (36.3:62.7:1.0) Comparative fluoroethylenecarbonate + — 0.42 74 82 Example 19 diethyl carbonate (39.7:60.3)Comparative fluoroethylene carbonate + — 0.49 74 85 Example 20 diethylcarbonate + vinylene carbonate (39.3:59.7:1.0) Comparative ethylenecarbonate + — 0.35 68 76 Example 21 diethyl carbonate + ethyl(2,2-difluoroethyl) carbonate (39.3:59.7:1.0) Comparative ethylenecarbonate + — 0.47 69 80 Example 22 diethyl carbonate + ethyl(2,2-difluoroethyl) carbonate + vinylene carbonate (35.9:62.1:1.0:1.0)Comparative ethylene carbonate + — 0.33 70 80 Example 23ethyl-(2,2-difluoroethyl) carbonate (31.8:68.2) Comparative ethylenecarbonate + — 0.49 71 83 Example 24 ethyl-(2,2-difluoroethyl)carbonate + vinylene carbonate (31.5:67.5:1.0)

The following was ascertained as apparent from Table 6 to Table 8. Evenin the case of using a negative-electrode active material containingsilicon, which is a non-carbon material, the nonaqueous-electrolytesecondary batteries produced using the nonaqueous electrolytes 1 of theinvention (Example 56 of Nonaqueous Electrolyte 1 to Example 74 ofNonaqueous Electrolyte 1), which contained at least one carbonate havinga halogen atom and further contained a monofluorophosphate and/or adifluorophosphate, were inhibited from swelling during high-temperaturestorage and from deteriorating in battery characteristics represented byresidual capacity and recovery capacity as in the case of using a carbonmaterial as an active material, as compared with thenonaqueous-electrolyte secondary batteries produced using the nonaqueouselectrolytes containing one of these compounds (Comparative Example 14for Nonaqueous Electrolyte 1, Comparative Example 15 for NonaqueousElectrolyte 1, and Comparative Examples 17 to 24 for NonaqueousElectrolyte 1) or using the nonaqueous electrolytes containing neitherof those compounds (Comparative Examples 13 and 16 for NonaqueousElectrolyte 1). The same effect was observed also in the case of usingnonaqueous electrolytes containing vinylene carbonate, which is anexample of the specific carbonate.

Example 1 of Nonaqueous Electrolyte 2 Production ofNonaqueous-Electrolyte Secondary Battery

[Production of Positive Electrode]

A positive electrode was produced in the same manner as in [Productionof Positive Electrode] in Example 1 of Nonaqueous Electrolyte 1.

[Production of Negative Electrode]

A negative electrode was produced in the same manner as in [Productionof Negative Electrode] in Example 1 of Nonaqueous Electrolyte 1.

[Nonaqueous Electrolyte]

In a dry argon atmosphere, LiPF₆ which each had been sufficiently driedwas dissolved, in an amount of 1 mol/L, in a nonaqueous solvent preparedby mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), anddimethoxyethane (DME), which is “a compound which is liquid at 25° C.,has a permittivity of 5 or higher and a coefficient of viscosity of 0.6cP or lower, and has a group constituting a heteroelement-containingframework (excluding carbonyl group)”, in the proportion shown in Table9. Thus, a nonaqueous electrolyte was prepared. Furthermore, amonofluorophosphate and/or a difluorophosphate was dissolved in thesolution so as to result in the respective concentrations shown in Table9. Thus, a desired nonaqueous electrolyte was obtained.

[Fabrication of Nonaqueous-Electrolyte Secondary Battery]

A battery was produced in the same manner as in [Fabrication ofNonaqueous-Electrolyte Secondary Battery] in Example 1 of NonaqueousElectrolyte 1.

<Evaluation of Nonaqueous-Electrolyte Secondary Battery forHigh-Temperature Storability>

The battery in a sheet form was evaluated in the state of beingsandwiched between glass plates in order to enhance contact between theelectrodes. At 25° C., this battery was subjected to 3 cycles ofcharge/discharge at a constant current corresponding to 0.2 C and at afinal charge voltage of 4.2V and a final discharge voltage of 3V tostabilize the battery. In the fourth cycle, the battery was subjected to4.2V constant-current constant-voltage charge (CCCV charge) (0.05 Ccutting) in which the battery was charged to a final charge voltage of4.2V at a current corresponding to 0.5 C and further charged until thecharge current value reached a current value corresponding to 0.05 C.Thereafter, this battery was subjected to 3V discharge at a constantcurrent corresponding to 0.2 C to determine the discharge capacity ofthe battery before high-temperature storage. This battery was subjectedagain to 4.2V-CCCV (0.05 C cutting) charge and then stored at a hightemperature under the conditions of 85° C. and 24 hours.

Before and after the high-temperature storage, the sheet battery wasimmersed in an ethanol bath. The amount of the gas evolved wasdetermined from the resultant volume change. This gas amount was takenas “storage swell (mL)”. The battery which had undergone the storage wasdischarged at 25° C. and a constant current of 0.2 C to a finaldischarge voltage of 3V to obtain the “residual capacity (%)” after thestorage test. This battery was subjected again to 4.2V-CCCV (0.05 Ccutting) charge and then discharged to 3V at a current valuecorresponding to 0.2 C to determine the 0.2 C capacity and therebyobtain the 0.2 C capacity of the battery which had undergone the storagetest. This capacity was taken as “recovery capacity (%)”. This batterywas subjected once more to 4.2V-CCCV (0.05 C cutting) charge and thendischarged to 3V at a current value corresponding to 1 C to determinethe 1 C capacity and thereby obtain the 1 C capacity of the batterywhich had undergone the storage test. This capacity was divided by the0.2 C capacity, and the resultant quotient was taken as “loadcharacteristics (%)”.

In Table 9 are shown the storage swell (mL), the residual capacity (%)and recovery capacity (%), which are values when the discharge capacitybefore the high-temperature storage is taken as 100, and the loadcharacteristics (%). “1 C” means a current value at which the batterycan be fully charged by 1-hour charge.

Example 2 of Nonaqueous Electrolyte 2 to Example 10 of NonaqueousElectrolyte 2 and Comparative Example 4 for Nonaqueous Electrolyte 2

Desired nonaqueous electrolytes were prepared in the same manner as inExample 1 of Nonaqueous Electrolyte 2, except that the kinds andcontents of the nonaqueous solvent and the monofluorophosphate and/ordifluorophosphate were changed to those shown in Table 9.Nonaqueous-electrolyte secondary batteries were produced and thenevaluated for high-temperature storability in the same manner as inExample 1 of Nonaqueous Electrolyte 2. The results thereof are shown inTable 9.

Comparative Example 1 for Nonaqueous Electrolyte 2 to ComparativeExample 3 for Nonaqueous Electrolyte 2

Desired nonaqueous electrolytes were prepared in the same manner as inExample 1 of Nonaqueous Electrolyte 2, except that the nonaqueoussolvent only was used so as to result in the contents shown in Table 9.Nonaqueous-electrolyte secondary batteries were produced and thenevaluated for high-temperature storability in the same manner as inExample 1 of Nonaqueous Electrolyte 2. The results thereof are shown inTable 9.

Example 11 of Nonaqueous Electrolyte 2 to Example 12 of NonaqueousElectrolyte 2 and Comparative Example 5 for Nonaqueous Electrolyte 2 toComparative Example 7 for Nonaqueous Electrolyte 2

Desired nonaqueous electrolytes were prepared in the same manner as inExample 1 of Nonaqueous Electrolyte 2, except that the nonaqueoussolvent was used so as to result in the contents shown in Table 9 andthat vinylene carbonate (VC) was used in an amount of 1% by mass basedon the whole nonaqueous electrolyte. Nonaqueous-electrolyte secondarybatteries were produced and then evaluated for high-temperaturestorability in the same manner as in Example 1 of Nonaqueous Electrolyte2. The results thereof are shown in Table 9.

The symbols used for expressing nonaqueous solvents in Table 9 and thepermittivities and viscosity coefficients thereof are as follows.

EC: ethylene carbonate (permittivity, 90; viscosity coefficient, 1.9)

EMC: ethyl methyl carbonate (permittivity, 2.9; viscosity coefficient,0.7)

DME: dimethoxyethane (permittivity, 7.1; viscosity coefficient, 0.5)

EME: ethoxymethoxyethane (permittivity, 5.7; viscosity coefficient, 0.5)

DEE: diethoxyethane (permittivity, 5; viscosity coefficient, 0.6)

AN: acetonitrile (permittivity, 37.5; viscosity coefficient, 0.4)

PN: propionitrile (permittivity, 27.7; viscosity coefficient, 0.4)

TABLE 9 Addition of Results of evaluation of high-temperaturestorability Monofluorophosphate and/or vinylene Residual Recovery LoadNonaqueous solvent difluorophosphate carbonate Storage swell capacitycapacity characteristics No. (vol %) (mass %) (1 mass %) (mL) (%) (%)(%) Example 1 EC:EMC:DME = 30:60:10 lithium difluorophosphate (0.5) notadded 0.20 68 73 79 Example 2 EC:EMC:DME = 30:60:10 lithiumdifluorophosphate (0.1) not added 0.28 63 69 75 Example 3 EC:EMC:DME =30:60:10 lithium difluorophosphate (1.0) not added 0.16 70 75 82 Example4 EC:EMC:DME = 30:60:10 dilithium monofluorophosphate not added 0.33 5965 69 (0.1) Example 5 EC:EMC:EME = 30:60:10 lithium difluorophosphate(0.5) not added 0.16 70 74 77 Example 6 EC:EMC:DEE = 30:60:10 lithiumdifluorophosphate (0.5) not added 0.16 71 75 75 Example 7 EC:EMC:DME =30:65:5 lithium difluorophosphate (0.5) not added 0.15 71 76 74 Example8 EC:EMC:AN = 30:65:5 lithium difluorophosphate (0.5) not added 0.25 6567 82 Example 9 EC:EMC:AN = 30:60:10 lithium difluorophosphate (0.5) notadded 0.30 62 64 85 Example 10 EC:EMC:PN = 30:65:5 lithiumdifluorophosphate (0.5) not added 0.23 67 70 80 Example 11 EC:EMC:DME =30:60:10 lithium difluorophosphate (0.5) added 0.24 71 75 77 Example 12EC:EMC:AN = 30:65:5 lithium difluorophosphate (0.5) added 0.28 68 69 80Comparative EC:EMC = 30:70 none not added 0.18 70 74 60 Example 1Comparative EC:EMC:DME = 30:60:10 none not added Unable to be did notdid not work did not work Example 2 measured work Comparative EC:EMC:AN= 30:65:5 none not added Unable to be did not did not work did not workExample 3 measured work Comparative EC:EMC = 30:70 lithiumdifluorophosphate (0.5) not added 0.20 67 78 68 Example 4 ComparativeEC:EMC = 30:70 none added 0.37 75 85 64 Example 5 Comparative EC:EMC:DME= 30:60:10 none added 3.2  43 52 30 Example 6 Comparative EC:EMC:AN =30:65:5 none added 3.6  25 32 25 Example 7

The following is apparent from Table 9. The nonaqueous-electrolytesecondary batteries produced using the nonaqueous electrolytes of theinvention, which contained a “compound which was liquid at 25° C., had apermittivity of 5 or higher and a coefficient of viscosity of 0.6 cP orlower, and had a group constituting a heteroelement-containing framework(excluding carbonyl group)” according to this invention and furthercontained a monofluorophosphate and/or a difluorophosphate, wereinhibited from swelling during high-temperature storage beyond the rangewhere battery operation was possible and were further inhibited fromdeteriorating in battery characteristics represented by residualcapacity and recovery capacity, as compared with thenonaqueous-electrolyte secondary batteries produced using the nonaqueouselectrolytes containing one of those compounds or containing neither ofthose compounds, while retaining the advantage of keeping resistancelow, which advantage is inherent in the “compound which is liquid at 25°C., has a permittivity of 5 or higher and a coefficient of viscosity of0.6 cP or lower, and has a group constituting a heteroelement-containingframework (excluding carbonyl group)”. The batteries according to theinvention, on the other hand, retained high load characteristics.

Specifically, the nonaqueous electrolytes produced in Example 1 ofNonaqueous Electrolyte 2 to Example 10 of Nonaqueous Electrolyte 2compared favorably in swelling during high-temperature storage with thenonaqueous electrolytes produced in Comparative Example 1 for NonaqueousElectrolyte 2 and Comparative Example 4 for Nonaqueous Electrolyte 2,which contained a difluorophosphate only. Furthermore, these nonaqueouselectrolytes according to the invention were equal to or lower thanthese comparative nonaqueous electrolytes in the deterioration ofbattery characteristics. The nonaqueous electrolytes of the invention,on the other hand, enabled the batteries to retain high loadcharacteristics, which show an advantage inherent in the “compound whichis liquid at 25° C., has a permittivity of 5 or higher and a coefficientof viscosity of 0.6 cP or lower, and has a group constituting aheteroelement-containing framework (excluding carbonyl group)” accordingto the invention. The batteries of Comparative Example 2 for NonaqueousElectrolyte 2 and Comparative Example 3 for Nonaqueous Electrolyte 2, inwhich a “compound which was liquid at 25° C., had a permittivity of 5 orhigher and a coefficient of viscosity of 0.6 cP or lower, and had agroup constituting a heteroelement-containing framework (excludingcarbonyl group)” only was contained, deteriorated to such a degree thatthe batteries did not work. The difference between the batteries of theExamples and those of the Comparative Examples is clear.

Furthermore, as apparent from Comparative Example 6 for NonaqueousElectrolyte 2 to Comparative Example 7 for Nonaqueous Electrolyte 2, thebatteries, in which the nonaqueous electrolytes contained vinylenecarbonate (VC) as an example of the specific carbonate, continuedworking in a certain degree. However, a comparison between theseComparative Examples and Example 1 of Nonaqueous Electrolyte 2 toExample 10 of Nonaqueous Electrolyte 2 shows that there is a largedifference in load characteristics. This is because the coexistence ofthe three ingredients, i.e., a “compound which is liquid at 25° C., hasa permittivity of 5 or higher and a coefficient of viscosity of 0.6 cPor lower, and has a group constituting a heteroelement-containingframework (excluding carbonyl group)”, a difluorophosphoric acid, andvinylene carbonate, produced a further effect as in Example 11 ofNonaqueous Electrolyte 2 and Example 12 of Nonaqueous Electrolyte 2.

Examples of Nonaqueous Electrolyte 3 and Comparative Examples forNonaqueous Electrolyte 3

The nonaqueous-electrolyte secondary batteries obtained in the followingExamples of Nonaqueous Electrolyte 3 and Comparative Examples forNonaqueous Electrolyte 3 were evaluated by the methods shown below.

<Measurement of Initial Discharge Capacity>

Each nonaqueous-electrolyte secondary battery was evaluated in the stateof being sandwiched between glass plates in order to enhance contactbetween the electrodes. At 25° C., this battery was charged to 4.2V at aconstant current corresponding to 0.2 C and then discharged to 3V at aconstant current of 0.2 C. Three cycles of this charge/discharge wereconducted to stabilize the battery. In the fourth cycle, the battery wascharged to 4.2V at a constant current of 0.5 C, subsequently charged ata constant voltage of 4.2V until the current value reached 0.05 C, andthen discharged to 3V at a constant current of 0.2 C to determineinitial discharge capacity. “1 C” means a current value at which thereference capacity of the battery is discharged over 1 hour; “0.2 C”means the current value which is ⅕ the 1 C.

<Evaluation of Continuous-Charge Characteristics>

The nonaqueous-electrolyte secondary battery which had undergone thecapacity evaluation test was immersed in an ethanol bath to measure thevolume thereof. Thereafter, at 60° C., the battery was subjected toconstant-current charge at a constant current of 0.5 C and, at the timewhen the voltage had reached 4.25V, the constant-current charge waschanged to constant-voltage charge to conduct continuous charge for 1week. This battery was cooled and then immersed in an ethanol bath tomeasure the volume thereof. The amount of the gas which had generatedwas determined from the volume change through the continuous charge.This gas amount was taken as “amount of gas evolved through continuouscharge (mL)”. After the determination of the amount of the gas evolved,the battery was discharged to 3V at 25° C. and a constant current of 0.2C. Subsequently, this battery was charged to 4.2V at a constant currentof 0.5 C, thereafter charged at a constant voltage of 4.2V until thecurrent value reached 0.05 C, and then discharged to 3V at a constantcurrent of 1 C to determine the 1 C discharge capacity of the batterywhich had undergone the continuous-charge test. The proportion of this 1C discharge capacity after the continuous-charge test to the initialdischarge capacity was determined, and this proportion was taken as “1 Cdischarge capacity after continuous charge (%)”.

Example 1 of Nonaqueous Electrolyte 3 Production ofNonaqueous-Electrolyte Secondary Battery

[Production of Negative Electrode]

Ninety-four parts by weight of a natural-graphite powder having a dvalue for the lattice plane (002) and a crystallite size (Lc), bothdetermined by X-ray diffractometry, of 0.336 nm and 652 nm,respectively, an ash content of 0.07 parts by weight, a median diameteras determined by the laser diffraction/scattering method of 12 μm, aspecific surface area as determined by the BET method of 7.5 m²/g, an Rvalue (=I_(B)/I_(A)) as determined by Raman spectroscopy using an argonion laser light of 0.12, and a half-value width for a peak in1,570-1,620 cm⁻¹ range of 19.9 cm⁻¹ was mixed with 6 parts by weight ofpoly(vinylidene fluoride). N-Methyl-2-pyrrolidone was added to themixture to slurry it. This slurry was evenly applied to one side of acopper foil having a thickness of 12 μm and dried. Thereafter, thecoated foil was pressed so as to result in a negative-electrodeactive-material layer having a density of 1.67 g/cm³. Thus, a negativeelectrode was obtained.

[Production of Positive Electrode]

Ninety percent by mass lithium cobalt oxide (LiCoO₂) as apositive-electrode active material was mixed with 4% by mass carbonblack and 6% by mass poly(vinylidene fluoride) (trade name “KF-1000”,manufactured by Kureha Chemical). N-Methyl-2-pyrrolidone was added tothe mixture to slurry it. This slurry was applied to each side of analuminum foil having a thickness of 15 μm and dried. Thereafter, thecoated foil was pressed so as to result in positive-electrodeactive-material layers having a density of 3.2 g/cm³. Thus, a positiveelectrode was obtained.

[Nonaqueous Electrolyte]

In a dry argon atmosphere, sufficiently dried LiPF₆ and vinylenecarbonate were added, in concentrations of 1 mol/L and 2% by massrespectively, to a mixture of ethylene carbonate, ethyl methylcarbonate, and dimethyl carbonate (volume ratio, 2:4:4). Themonofluorophosphate and/or difluorophosphate and the “compound A of theinvention” were dissolved therein so as to result in the respectiveconcentrations shown in Table 10. Thus, a desired nonaqueous electrolytewas obtained.

[Production of Nonaqueous-Electrolyte Secondary Battery]

The positive electrode and negative electrode described above and aseparator made of polyethylene were superposed in the order of negativeelectrode/separator/positive electrode/separator/negative electrode toproduce a battery element. This battery element was inserted into a bagconstituted of a laminated film obtained by coating both sides ofaluminum (thickness, 40 μm) with a resin layer, with terminals of thepositive and negative electrodes projecting outward. Thereafter, thenonaqueous electrolyte was introduced into the bag, and this bag wasvacuum-sealed to produce a sheet battery. This battery was subjected tothe evaluation of continuous-charge characteristics described above. Theresults thereof are shown in Table 10.

Example 2 of Nonaqueous Electrolyte 3 to Example 10 of NonaqueousElectrolyte 3 and Comparative Example 1 for Nonaqueous Electrolyte 3 toComparative Example 4 for Nonaqueous Electrolyte 3

Desired nonaqueous electrolytes were prepared in the same manner as inExample 1 of Nonaqueous Electrolyte 3, except that the“monofluorophosphate and/or difluorophosphate” and “compound of theinvention” shown in Table 10 were replaced with the kinds shown in Table10 and used so as to result in the contents shown in Table 10.Nonaqueous-electrolyte secondary batteries were produced and thenevaluated for continuous-charge characteristics in the same manner as inExample 1 of Nonaqueous Electrolyte 3. The results thereof are shown inTable 10.

TABLE 10 Amount of gas 1 C discharge evolved through capacity afterMonofluorophosphate and/or continuous continuous difluorophosphateCompound of the invention charge charge No. (mass %) (mass %) (mL) (%)Example 1 Lithium difluorophosphate ethyl diethylphosphinate 0.39 67(0.5) (0.5) Example 2 Lithium difluorophosphate Succinonitrile 0.36 61(0.5) (0.5) Example 3 Lithium difluorophosphate methyl isocyanate 0.4565 (0.5) (0.5) Example 4 Lithium difluorophosphateHexafluorotricyclophosphazene 0.39 64 (0.5) (0.5) Example 5 Lithiumdifluorophosphate 1,4-butanediol bis(2,2,2- 0.40 65 (0.5)trifluoroethanesulfonate) (0.5) Example 6 Lithium difluorophosphatedi-n-butyl sulfide 0.44 64 (0.5) (0.2) Example 7 Lithiumdifluorophosphate di-n-butyl disulfide 0.43 64 (0.5) (0.2) Example 8Lithium difluorophosphate succinic anhydride 0.41 66 (0.5) (0.3) Example9 Lithium difluorophosphate α-methyl-γ-butyrolactone 0.42 65 (0.5) (0.5)Example 10 Lithium difluorophosphate 2-propynyl acetate 0.44 64 (0.5)(0.5) Comparative — — 0.53 62 Example 1 Comparative Lithiumdifluorophosphate — 0.51 61 Example 2 (0.5) Comparative — ethyldiethylphosphinate 0.54 64 Example 3 (0.5) Comparative — Succinonitrile0.40 48 Example 4 (0.5)

The following is apparent from Table 10. The nonaqueous-electrolytesecondary batteries produced using the nonaqueous electrolytes of theinvention, which contained a “compound A of the invention” and furthercontained a monofluorophosphate and/or difluorophosphate (Example 1 ofNonaqueous Electrolyte 3 to Example 10 of Nonaqueous Electrolyte 3),were inhibited from suffering gas evolution and battery characteristicsdeterioration during continuous charge as compared with thenonaqueous-electrolyte secondary batteries produced using the nonaqueouselectrolytes containing one of those compounds (Comparative Example 2for Nonaqueous Electrolyte 3 to Comparative Example 4 for NonaqueousElectrolyte 3) or using the nonaqueous electrolyte containing neither ofthose compounds (Comparative Example 1 for Nonaqueous Electrolyte 3).

The batteries obtained in the following Examples of NonaqueousElectrolyte 4 and Comparative Examples for Nonaqueous Electrolyte 4 wereevaluated by the methods shown below.

[Evaluation of Initial Discharge Capacity]

Each lithium secondary battery was evaluated in the state of beingsandwiched between glass plates in order to enhance contact between theelectrodes. At 25° C., this battery was charged to 4.2V at a constantcurrent corresponding to 0.2 C and then discharged to 3V at a constantcurrent of 0.2 C. Three cycles of this charge/discharge were conductedto stabilize the battery. In the fourth cycle, the battery was chargedto 4.2V at a constant current of 0.5 C, subsequently charged at aconstant voltage of 4.2V until the current value reached 0.05 C, andthen discharged to 3V at a constant current of 0.2 C to determineinitial discharge capacity. “1 C” means a current value at which thereference capacity of the battery is discharged over 1-hour; “2 C” meansthe current value two times the 1 C and “0.2 C” means the current valuewhich is ⅕ the 1 C.

[Evaluation of 2 C Discharge Capacity]

The battery which had undergone the test for evaluating initialdischarge capacity was subjected at 25° C. to a test in which thebattery was charged to 4.2V at a constant current of 0.5 C, subsequentlycharged at a constant voltage of 4.2V until the current value reached0.05 C, and discharged to 3V at a constant current of 2 C. Theproportion of the resultant discharge capacity (%) to the dischargecapacity determined through the test for initial discharge capacity,which was taken as 100, was determined.

[Evaluation of High-Temperature Storability]

The battery which had undergone the capacity evaluation tests wascharged to 4.2V at a constant current of 0.5 C and then charged at aconstant voltage of 4.2V until the current value reached 0.05 C. Thisbattery was stored at 85° C. for 24 hours and then cooled. Thereafter,this battery was subjected at 25° C. to a test in which the battery wasdischarged to 3V at a constant current of 0.2 C, charged to 4.2V at aconstant current of 0.5 C, subsequently charged at a constant voltage of4.2V until the current value reached 0.05 C, and then discharged to 3Vat a constant current of 2 C. The proportion of the resultant dischargecapacity (%) to the discharge capacity determined through the test forinitial discharge capacity, which was taken as 100, was determined.

[Evaluation of Thermal Stability]

The battery was charged to 4.2V at a constant current corresponding to0.2 C and then discharged to 3V at a constant current of 0.2 C. Threecycles of this charge/discharge were conducted to stabilize the battery.In the fourth cycle, the battery was charged to 4.2V at a constantcurrent of 0.5 C and then charged at a constant voltage of 4.2V untilthe current value reached 0.05 C. The quantity of exothermic heat ofthis battery in a charged state was measured with a Calvet calorimeterover the range of from room temperature to 300° C.

Example 1 of Nonaqueous Electrolyte 4 Production of Negative Electrode

To 98 parts by weight of artificial-graphite powder KS-44 (trade name;manufactured by Timcal) were added 100 parts by weight of an aqueousdispersion of sodium carboxymethyl cellulose (concentration of sodiumcarboxymethyl cellulose, 1% by mass) as a thickener and 2 parts byweight of an aqueous dispersion of a styrene/butadiene rubber(concentration of styrene/butadiene rubber, 50% by mass) as a binder.The ingredients were mixed together by means of a disperser to obtain aslurry. The slurry obtained was applied to one side of a copper foilhaving a thickness of 10 μm and dried. This coated foil was rolled witha pressing machine to a thickness of 75 μm, and a piece of a shapehaving an active-material layer size with a width of 30 mm and a lengthof 40 mm and having an uncoated area with a width of 5 mm and a lengthof 9 mm was cut out of the rolled sheet. Thus, a negative electrode wasobtained.

[Production of Positive Electrode]

Ninety percent by mass lithium cobalt oxide (LiCoO₂) as apositive-electrode active material was mixed with 5% by mass acetyleneblack as a conductive material and 5% by mass poly(vinylidene fluoride)(PVdF) as a binder in N-methylpyrrolidone solvent to obtain a slurry.The slurry obtained was applied to one side of an aluminum foil having athickness of 15 μm and dried. This coated foil was rolled with apressing machine to a thickness of 80 μm, and a piece of a shape havingan active-material layer size with a width of 30 mm and a length of 40mm and having a uncoated area with a width of 5 mm and a length of 9 mmwas cut out of the rolled sheet. Thus, a positive electrode wasobtained.

[Production of Electrolyte]

In a dry argon atmosphere, 98 parts by weight of a mixture of sulfolane(SLF) and ethyl methyl carbonate (EMC; coefficient of viscosity at 25°C., 0.68 mPa·s) (volume ratio, 3:7) was mixed with 2 parts by weight ofvinylene carbonate (VC). Subsequently, sufficiently dried LiPF₆ wasdissolved therein so as to result in a proportion of 1.0 mol/L. Thus, anelectrolyte was obtained.

[Production of Nonaqueous-Electrolyte Battery]

The positive electrode and negative electrode described above and aseparator made of polyethylene were superposed in the order of negativeelectrode/separator/positive electrode to produce a battery element.This battery element was inserted into a bag constituted of a laminatedfilm obtained by coating both sides of aluminum (thickness, 40 μm) witha resin layer, with terminals of the positive and negative electrodesprojecting outward. Thereafter, the electrolyte was introduced into thebag, and this bag was vacuum-sealed to produce a sheet battery. Thisbattery was evaluated. The components of the electrolyte and the resultsof the evaluation are shown in Table 11 and Table 12.

Example 2 of Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except thatvinylethylene carbonate (VEC) was used in place of the vinylenecarbonate (VC) in the electrolyte of Example 1 of Nonaqueous Electrolyte4. The components of the electrolyte and the results of the evaluationare shown in Table 11 and Table 12.

Example 3 of Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except thatfluoroethylene carbonate (FEC) was used in place of the vinylenecarbonate (VC) in the electrolyte of Example 1 of Nonaqueous Electrolyte4. The components of the electrolyte and the results of the evaluationare shown in Table 11 and Table 12.

Example 4 of Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except that0.5 parts by weight of LiPO₂F₂ was used in place of the vinylenecarbonate (VC) in the electrolyte of Example 1 of Nonaqueous Electrolyte4. The components of the electrolyte and the results of the evaluationare shown in Table 11 and Table 12.

Comparative Example 1 for Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except thatuse was made of an electrolyte produced by dissolving sufficiently driedLiPF₆ in a mixture of sulfolane (SLF) and ethyl methyl carbonate (EMC)(volume ratio, 3:7) so as to result in a proportion of 1.0 mol/L. Thecomponents of the electrolyte and the results of the evaluation areshown in Table 11 and Table 12.

Comparative Example 2 for Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except thatuse was made of an electrolyte produced by mixing 94 parts by weight ofa mixture of sulfolane (SLF) and γ-butyrolactone (GBL; coefficient ofviscosity at 25° C., 1.73 mPa·s) (volume ratio, 3:7) with 2 parts byweight of vinylene carbonate (VC), 2 parts by weight of vinylethylenecarbonate (VEC), and 2 parts by weight of trioctyl phosphate (TOP) andthen dissolving sufficiently dried LiPF₆ therein so as to result in aproportion of 1.0 mol/L. The components of the electrolyte and theresults of the evaluation are shown in Table 11 and Table 12.

Comparative Example 3 for Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except thatuse was made of an electrolyte produced by mixing 94 parts by weight ofa mixture of sulfolane (SLF) and γ-butyrolactone (GBL) (volume ratio,3:7) with 2 parts by weight of vinylene carbonate (VC), 2 parts byweight of vinylethylene carbonate (VEC), and 2 parts by weight oftrioctyl phosphate (TOP) and then dissolving sufficiently dried LiBF₄therein so as to result in a proportion of 1.0 mol/L. The components ofthe electrolyte and the results of the evaluation are shown in Table 11and Table 12.

Comparative Example 4 for Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except thatuse was made of an electrolyte produced by mixing 98 parts by weight ofa mixture of γ-butyrolactone (GBL) and ethyl methyl carbonate (EMC)(volume ratio, 3:7) with 2 parts by weight of vinylene carbonate (VC)and then dissolving sufficiently dried LiPF₆ therein so as to result ina proportion of 1.0 mol/L. The components of the electrolyte and theresults of the evaluation are shown in Table 11 and Table 12.

Comparative Example 5 for Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced and evaluated in thesame manners as in Example 1 of Nonaqueous Electrolyte 4, except thatuse was made of an electrolyte produced by mixing 98 parts by weight ofa mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC)(volume ratio, 3:7) with 2 parts by weight of vinylene carbonate (VC)and then dissolving sufficiently dried LiPF₆ therein so as to result ina proportion of 1.0 mol/L. The components of the electrolyte and theresults of the evaluation are shown in Table 11 and Table 12.

TABLE 11 Electrolyte Solvent Example 1 LiPF₆ SLF + EMC + VC Example 2LiPF₆ SLF + EMC + VEC Example 3 LiPF₆ SLF + EMC + FEC Example 4 LiPF₆SLF + EMC + LiPO₂F₂ Comparative Example 1 LiPF₆ SLF + EMC ComparativeExample 2 LiPF₆ SLF + GBL + VC + VEC + TOP Comparative Example 3 LiBF₄SLF + GBL + VC + VEC + TOP Comparative Example 4 LiPF₆ GBL + EMC + VCComparative Example 5 LiPF₆ EC + EMC + VC

TABLE 12 2 C discharge 2 C discharge capacity before 85° C. capacityafter 85° C. storage (%) storage (%) Example 1 83.1 82.6 Example 2 82.581.8 Example 3 87.4 80.8 Example 4 89.7 85.5 Comparative Example 1 66.155.4 Comparative Example 2 48.3 3.4 Comparative Example 3 26.0 14.1Comparative Example 4 89.8 70.2 Comparative Example 5 89.1 84.7

Example 5 of Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced using the positiveelectrode, negative electrode, and electrolyte obtained by the samemethods as in Example 3 of Nonaqueous Electrolyte 4. This battery wasevaluated for thermal stability by thermal analysis. The results of theevaluation are shown in Table 13.

Comparative Example 6 for Nonaqueous Electrolyte 4

A sheet-form lithium secondary battery was produced using the positiveelectrode, negative electrode, and electrolyte obtained by the samemethods as in Comparative Example 4 for Nonaqueous Electrolyte 4. Thisbattery was evaluated for thermal stability by thermal analysis. Theresults of the evaluation are shown in Table 13.

TABLE 13 Quantity of exothermic heat (J) Example 5 382 ComparativeExample 6 605

The following was found as apparent from Table 11 to Table 13. Thebatteries employing the nonaqueous electrolytes according to theinvention (Examples 1 to 4 of Nonaqueous Electrolyte 4) were excellentin high-current-density charge/discharge characteristics andhigh-temperature storability and further had high safety as can be seenfrom the small quantity of exothermic heat of the battery of Example 5of Nonaqueous Electrolyte 4. On the other hand, the batteries employingthe nonaqueous electrolytes which were not nonaqueous electrolytes ofthe invention (Comparative Example 1 for Nonaqueous Electrolyte toComparative Example 5 for Nonaqueous Electrolyte 4) were inferior incharge/discharge characteristics and high-temperature storability andhad a large quantity of exothermic heat as in Comparative Example 6 forNonaqueous Electrolyte 4.

[Production of Positive Electrode]

Ninety-two parts by weight of a lithium-transition metal composite oxidecontaining nickel, manganese, and cobalt(LiNi_(0.33)Mn_(0.33)Co_(0.33)O₂) was mixed with 4 parts by weight ofpoly(vinylidene fluoride) (hereinafter suitably referred to as “PVdF”)and 4 parts by weight of acetylene black. N-Methylpyrrolidone was addedto the mixture to slurry it. This slurry was applied to each side of acurrent collector made of aluminum, and dried. Thus, a positiveelectrode was obtained.

[Production of Negative Electrode]

Ninety-two parts by weight of a graphite powder was mixed with 8 partsby weight of PVdF. N-Methylpyrrolidone was added to the mixture toslurry it. This slurry was applied to one side of a current collectormade of copper, and dried. Thus, a negative electrode was obtained.

[Production of Nonaqueous-Electrolyte Secondary Battery]

The positive electrode and negative electrode described above and aseparator made of polyethylene were superposed in the order of negativeelectrode/separator/positive electrode/separator/negative electrode. Thebattery element thus obtained was wrapped in a cylindricalaluminum-laminated film. The electrolyte which will be described laterwas introduced into this package, which was then vacuum-sealed. Thus, asheet-form nonaqueous-electrolyte secondary battery was produced.Furthermore, this sheet battery was pressed by being sandwiched betweenglass plates, in order to enhance contact between the electrodes.

[Capacity Evaluation]

In a 25° C. thermostatic chamber, the sheet-form nonaqueous-electrolytesecondary battery was subjected to constant-current constant-voltagecharge (hereinafter suitably referred to as “CCCV charge”) to 4.4V at0.2 C and then discharged to 2.75 V at 0.2 C. This operation wasrepeated three times to conduct conditioning. Thereafter, this batterywas subjected again to CCCV charge to 4.4V at 0.2 C and discharged againto 2.75 V at 1 C to determine initial discharge capacity. The cutoffcurrent in each charging operation was set at 0.05 C. Incidentally, “1C” means a current value at which the whole capacity of the battery isdischarged over 1 hour.

[Evaluation of 4.4V Continuous-Charge Characteristics]

The battery which had undergone the capacity evaluation test was placedin a 60° C. thermostatic chamber and subjected to constant-currentcharge at 0.2 C. At the time when the voltage had reached 4.4V, theconstant-current charge was changed to constant-voltage charge. Thebattery was charged for 7 days and then cooled to 25° C. Subsequently,this battery was immersed in an ethanol bath to measure the buoyancy(Archimedes' principle), and the amount of the gas evolved wasdetermined from the buoyancy. Furthermore, the degree of deteriorationin capacity through the continuous charge was evaluated in the followingmanner. The battery was first discharged to 3V at 0.2 C, subsequentlysubjected to CCCV charge to 4.4V at 0.2 C, and then discharged to 2.75 Vat 1 C to measure the discharge capacity (recovery capacity) in thisdischarge. The capacity retention after the continuous charge wasdetermined according to the following calculation equation. The largerthe value of this property, the lower the deterioration of the battery.Capacity retention after continuous 7-day charge(%)=[(recovery capacityafter continuous 7-day charge)/(initial discharge capacity)]×100

Example 1 of Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of ethylene carbonate (EC) as a cyclic carbonateand ethyl methyl carbonate (EMC) as an acyclic carbonate (mixing volumeratio, 2:8; weight ratio, 24.7:75.3). This solution is referred to asbase electrolyte (I). A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane and vinylene carbonate (VC) to thebase electrolyte (I) so as to result in concentrations of 0.1% by massand 1% by mass, respectively, based on the nonaqueous electrolyte. Usingthis nonaqueous electrolyte, a nonaqueous-electrolyte secondary batterywas produced by the method described above. This battery was subjectedto the capacity evaluation and the evaluation of 4.4V continuous-chargecharacteristics. The results thereof are shown in Table 14.

Example 2 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane and fluoroethylene carbonate (FEC) tothe base electrolyte (I) so as to result in concentrations of 0.1% bymass and 1% by mass, respectively, based on the nonaqueous electrolyte.Using this nonaqueous electrolyte, a nonaqueous-electrolyte secondarybattery was produced by the method described above. This battery wassubjected to the capacity evaluation and the evaluation of 4.4Vcontinuous-charge characteristics. The results thereof are shown inTable 14.

Example 3 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane and lithium difluorophosphate(LiPO₂F₂) to the base electrolyte (I) so as to result in concentrationsof 0.1% by mass and 0.5% by mass, respectively, based on the nonaqueouselectrolyte. Using this nonaqueous electrolyte, a nonaqueous-electrolytesecondary battery was produced by the method described above. Thisbattery was subjected to the capacity evaluation and the evaluation of4.4V continuous-charge characteristics. The results thereof are shown inTable 14.

Example 4 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane to the base electrolyte (I) so as toresult in a concentration of 0.02% by mass based on the nonaqueouselectrolyte. Using the nonaqueous electrolyte obtained, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

Example 5 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane to the base electrolyte (I) so as toresult in a concentration of 0.05% by mass based on the nonaqueouselectrolyte. Using this nonaqueous electrolyte, a nonaqueous-electrolytesecondary battery was produced by the method described above. Thisbattery was subjected to the capacity evaluation and the evaluation of4.4V continuous-charge characteristics. The results thereof are shown inTable 14.

Example 6 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane to the base electrolyte (I) so as toresult in a concentration of 0.1% by mass based on the nonaqueouselectrolyte. Using this nonaqueous electrolyte, a nonaqueous-electrolytesecondary battery was produced by the method described above. Thisbattery was subjected to the capacity evaluation and the evaluation of4.4V continuous-charge characteristics. The results thereof are shown inTable 14.

Example 7 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,7,10-tetraazacyclododecane to the base electrolyte (I) so as toresult in a concentration of 0.1% by mass based on the nonaqueouselectrolyte. Using this nonaqueous electrolyte, a nonaqueous-electrolytesecondary battery was produced by the method described above. Thisbattery was subjected to the capacity evaluation and the evaluation of4.4V continuous-charge characteristics. The results thereof are shown inTable 14.

Example 8 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane to the baseelectrolyte (I) so as to result in a concentration of 0.1% by mass basedon the nonaqueous electrolyte. Using this nonaqueous electrolyte, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

Example 9 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane-5,7-dione to the base electrolyte (I)so as to result in a concentration of 0.1% by mass based on thenonaqueous electrolyte. Using this nonaqueous electrolyte, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

Example 10 of Nonaqueous Electrolyte 5

A nonaqueous electrolyte was prepared by addingcyclo(β-alanylglycyl-β-alanylglycyl) to the base electrolyte (I) so asto result in a concentration of 0.02% by mass based on the nonaqueouselectrolyte. Using this nonaqueous electrolyte, a nonaqueous-electrolytesecondary battery was produced by the method described above. Thisbattery was subjected to the capacity evaluation and the evaluation of4.4V continuous-charge characteristics. The results thereof are shown inTable 14.

Example 11 of Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of ethylene carbonate (EC) as a cyclic carbonateand ethyl methyl carbonate (EMC) as an acyclic carbonate (mixing volumeratio, 1:9; weight ratio, 12.7:87.3). This solution is referred to asbase electrolyte (II). A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane to the base electrolyte (II) so as toresult in a concentration of 0.1% by mass based on the nonaqueouselectrolyte. Using the nonaqueous electrolyte obtained, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

Example 12 of Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of fluoroethylene carbonate (FEC) as a cycliccarbonate and ethyl methyl carbonate (EMC) as an acyclic carbonate(mixing volume ratio, 1:9; weight ratio, 14.2:85.8). This solution isreferred to as base electrolyte (III). A nonaqueous electrolyte wasprepared by adding 1,4,8,11-tetraazacyclotetradecane to the baseelectrolyte (III) so as to result in a concentration of 0.1% by massbased on the nonaqueous electrolyte. Using the nonaqueous electrolyteobtained, a nonaqueous-electrolyte secondary battery was produced by themethod described above. This battery was subjected to the capacityevaluation and the evaluation of 4.4V continuous-charge characteristics.The results thereof are shown in Table 14.

Example 13 of Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of ethylene carbonate (EC) as a cyclic carbonateand ethyl methyl carbonate (EMC) as an acyclic carbonate (mixing volumeratio, 3:7; weight ratio, 36.0:64.0). This solution is referred to asbase electrolyte (IV). A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane to the base electrolyte (IV) so as toresult in a concentration of 0.1% by mass based on the nonaqueouselectrolyte. Using the nonaqueous electrolyte obtained, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

Example 14 of Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of ethylene carbonate (EC) as a cyclic carbonateand ethyl methyl carbonate (EMC) as an acyclic carbonate (mixing volumeratio, 4:6; weight ratio, 46.7:53.4). This solution is referred to asbase electrolyte (V). A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane-5,7-dione to the base electrolyte (V)so as to result in a concentration of 0.1% by mass based on thenonaqueous electrolyte. Using the nonaqueous electrolyte obtained, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

Example 15 of Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of ethylene carbonate (EC) and propylenecarbonate (PC) as cyclic carbonates (mixing volume ratio, 5:5; weightratio, 52.4:47.6). This solution is referred to as base electrolyte(VI). A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane-5,7-dione to the base electrolyte (VI)so as to result in a concentration of 0.1% by mass based on thenonaqueous electrolyte. Using the nonaqueous electrolyte obtained, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14. It can be seen that when a cyclicpolyamide compound has been added, there is no limitation on the weightratio of cyclic carbonates usable as solvents.

Comparative Example 1 for Nonaqueous Electrolyte 5

Using the base electrolyte (I) by itself, a nonaqueous-electrolytesecondary battery was produced by the method described above. Thisbattery was subjected to the capacity evaluation and the evaluation of4.4V continuous-charge characteristics. The results thereof are shown inTable 14.

Comparative Example 2 for Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of ethylene carbonate (EC) as a cyclic carbonateand ethyl methyl carbonate (EMC) as an acyclic carbonate (mixing volumeratio, 35:65; weight ratio, 41.4:58.6). This solution is referred to asbase electrolyte (VII). A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane to the base electrolyte (VII) so as toresult in a concentration of 0.1% by mass based on the nonaqueouselectrolyte. Using the nonaqueous electrolyte obtained, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

Comparative Example 3 for Nonaqueous Electrolyte 5

LiPF₆ as an electrolyte was dissolved, in a proportion of 1 mol/L, in amixed solvent composed of ethylene carbonate (EC) as a cyclic carbonateand ethyl methyl carbonate (EMC) as an acyclic carbonate (mixing volumeratio, 4:6; weight ratio, 46.7:53.4). This solution is referred to asbase electrolyte (V). A nonaqueous electrolyte was prepared by adding1,4,8,11-tetraazacyclotetradecane to the base electrolyte (V) so as toresult in a concentration of 0.1% by mass based on the nonaqueouselectrolyte. Using the nonaqueous electrolyte obtained, anonaqueous-electrolyte secondary battery was produced by the methoddescribed above. This battery was subjected to the capacity evaluationand the evaluation of 4.4V continuous-charge characteristics. Theresults thereof are shown in Table 14.

TABLE 14 Cyclic polyamine Specific After compound or cyclic compoundcontinuous-charge test polyamide compound (mass % based NonaqueousNonaqueous Capacity (mass % based on on nonaqueous organic solventorganic solvent Gas amount retention No. nonaqueous electrolyte)electrolyte) (volume ratio) (mass ratio) (mL) (%) Example 1 cyclam 0.1%VC 1% EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.32 65.6 Example 2 cyclam 0.1%FEC 1% EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.33 67.5 Example 3 cyclam 0.1%LiPO₂F₂ 0.5% EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.19 70.6 Example 4 cyclam0.02% none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.24 63.8 Example 5 cyclam0.05% none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.23 65.0 Example 6 cyclam0.1% none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.28 61.9 Example 7 cyclen0.1% none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.27 55.6 Example 8 TM-cyclam0.1% none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.18 53.8 Example 9 DO-cyclam0.1% none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.28 64.4 Example 10TetO-cyclam 0.02% none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.22 65.0 Example11 cyclam 0.1% none EC/EMC = 1/9 EC/EMC = 12.7/87.3 0.20 61.3 Example 12cyclam 0.1% none FEC/EMC = 1/9 FEC/EMC = 14.2/85.8 0.32 66.3 Example 13cyclam 0.1% none EC/EMC = 3/7 EC/EMC = 36.0/64.0 0.35 60.0 Example 14DO-cyclam 0.1% none EC/EMC = 4/6 EC/EMC = 46.7/53.4 0.35 56.9 Example 15DO-cyclam 0.1% none EC/PC = 5/5 EC/PC = 52.4/47.6 0.39 59.4 Comparativenone none EC/EMC = 2/8 EC/EMC = 24.7/75.3 0.82 43.8 Example 1Comparative cyclam 0.1% none EC/EMC = 35/65 EC/EMC = 41.4/58.6 0.71 48.1Example 2 Comparative cyclam 0.1% none EC/EMC = 4/6 EC/EMC = 46.7/53.40.98 40.6 Example 3

The symbols each used for expressing a cyclic polyamine compound orcyclic polyamide compound in Table 14 are as follows.

cyclam: 1,4,8,11-tetraazacyclotetradecane

cyclen: 1,4,7,10-tetraazacyclododecane

TM-cyclam: 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane

DO-cyclam: 1,4,8,11-tetraazacyclotetradecane-5,7-dione

TetO-cyclam: cyclo(β-alanylglycyl-β-alanylglycyl)

In Table 14, the “specific compound” means “at least one compoundselected from the group consisting of unsaturated carbonates,fluorine-containing carbonates, monofluorophosphates, anddifluorophosphates”. The symbols used for expressing “specificcompounds” are as follows.

VC: vinylene carbonate

FEC: fluoroethylene carbonate

LiPO₂F₂: lithium difluorophosphate

The following is apparent from Table 14. Use of the nonaqueouselectrolytes according to the invention improved continuous-chargecharacteristics (Examples 1 to 15 of Nonaqueous Electrolyte 5). On theother hand, in the case of the nonaqueous electrolytes which were notnonaqueous electrolytes according to the invention (i.e., in the case ofthe nonaqueous electrolytes falling under none of embodiment 5-1,embodiment 5-2, and embodiment 5-3), the batteries were inferior incontinuous-charge characteristics (Comparative Examples 1 to 3 forNonaqueous Electrolyte 5). Furthermore, in the case of the nonaqueousorganic solvents which contained a cyclic polyamine compound and furthercontained a cyclic carbonate in an amount exceeding 40% by mass as inComparative Example 2 for Nonaqueous Electrolyte 5 and ComparativeExample 3 for Nonaqueous Electrolyte 5, the batteries had poorcontinuous-charge characteristics.

<Production of Secondary Battery>

[Production of Positive Electrode]

A positive electrode was produced in the same manner as in [Productionof Positive Electrode] in Example 1 of Nonaqueous Electrolyte 1.

[Production of Negative Electrode]

A negative electrode was produced in the same manner as in [Productionof Negative Electrode] in Example 1 of Nonaqueous Electrolyte 1.

[Nonaqueous Electrolyte]

Example 1 of Nonaqueous Electrolyte 6

One mol/L LiPF₆, 0.05 mol/L lithium salt of cyclic1,2-perfluoroethanedisulfonylimide, which is the cyclic disulfonylimidesalt shown in Table 15, and 0.5% by mass lithium difluorophosphate whicheach had been sufficiently dried were dissolved in a mixture of ethylenecarbonate and ethyl methyl carbonate (volume ratio, 3:7) in a dry argonatmosphere. Thus, a desired nonaqueous electrolyte was obtained.

[Fabrication of Battery]

A battery was produced in the same manner as in [Fabrication of Battery]in Example 1 of Nonaqueous Electrolyte 1.

[Evaluation of Battery]

The battery in a sheet form was evaluated in the state of beingsandwiched between glass plates in order to enhance contact between theelectrodes. At 25° C., this battery was subjected to 3 cycles ofcharge/discharge at a constant current corresponding to 0.2 C and at afinal charge voltage of 4.2V and a final discharge voltage of 3V tostabilize the battery. In the fourth cycle, the battery was subjected to4.4V constant-current constant-voltage charge (CCCV charge) (0.05 Ccutting) in which the battery was charged to a final charge voltage of4.4V at a current corresponding to 0.5 C and further charged until thecharge current value reached a current value corresponding to 0.05 C.Thereafter, this battery was subjected to 3V discharge at a constantcurrent corresponding to 0.2 C to determine the discharge capacity ofthe battery before high-temperature storage. This battery was subjectedagain to 4.4V-CCCV (0.05 C cutting) charge and then stored at a hightemperature under the conditions of 85° C. and 24 hours.

Before and after the high-temperature storage, the sheet battery wasimmersed in an ethanol bath. The amount of the gas evolved wasdetermined from the resultant volume change. The battery which hadundergone the storage was discharged at 25° C. and a constant current of0.2 C to a final discharge voltage of 3V to obtain the residual capacityafter the storage test. This battery was subjected again to 4.4V-CCCV(0.05 C cutting) charge and then discharged to 3V at a current valuecorresponding to 0.2 C to determine the 0.2 C capacity and therebyobtain the 0.2 C capacity of the battery which had undergone the storagetest. This capacity was taken as recovery capacity. “1 C” means acurrent value at which the battery can be fully charged by 1-hourcharge. The residual capacity and recovery capacity (%) in the casewhere the discharge capacity as measured before the high-temperaturestorage is taken as 100 are shown in Table 15.

Example 2 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that thelithium salt of cyclic 1,2-perfluoroethanedisulfonylimide, which is acyclic disulfonylimide salt, was used in an amount of 0.1 mol/L. Thisbattery was evaluated, and the results thereof are shown in Table 15.

Example 3 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that thelithium salt of cyclic 1,2-perfluoroethanedisulfonylimide, which is acyclic disulfonylimide salt, was used in an amount of 0.01 mol/L. Thisbattery was evaluated, and the results thereof are shown in Table 15.

Example 4 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that thelithium salt of cyclic 1,2-perfluoroethanedisulfonylimide, which is acyclic disulfonylimide salt, was used in an amount of 0.05 mol/L. Thisbattery was evaluated, and the results thereof are shown in Table 15.

Example 5 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that thesodium salt of cyclic 1,2-perfluoroethanedisulfonylimide, which is acyclic disulfonylimide salt, was used in an amount of 0.05 mol/L. Thisbattery was evaluated, and the results thereof are shown in Table 15.

Example 6 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that lithiumdifluorophosphate was used in an amount of 0.1% by mass. This batterywas evaluated, and the results thereof are shown in Table 15.

Example 7 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that lithiumdifluorophosphate was used in an amount of 1.0% by mass. This batterywas evaluated, and the results thereof are shown in Table 15.

Example 8 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that sodiumdifluorophosphate was used in an amount of 0.5% by mass. This batterywas evaluated, and the results thereof are shown in Table 15.

Example 9 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that lithiummonofluorophosphate was used in an amount of 0.5% by mass. This batterywas evaluated, and the results thereof are shown in Table 15.

Example 10 of Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that adesired nonaqueous electrolyte was obtained by dissolving 1 mol/Lsufficiently dried LiPF₆, 0.05 mol/L lithium salt of cyclic1,2-perfloroethanedisulfonylimide, which is the cyclic disulfonylimidesalt shown in Table 15, 0.5% by mass lithium difluorophosphate, and 1part by weight of vinylene carbonate in a mixture of ethylene carbonateand ethyl methyl carbonate (volume ratio, 3:7) in a dry argonatmosphere. This battery was evaluated, and the results thereof areshown in Table 15.

Comparative Example 1 for Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that anonaqueous electrolyte was obtained by dissolving 1 mol/L sufficientlydried LiPF₆ in a mixture of ethylene carbonate and ethyl methylcarbonate (volume ratio, 3:7) in a dry argon atmosphere. This batterywas evaluated, and the results thereof are shown in Table 15.

Comparative Example 2 for Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that the 0.5%by mass lithium difluorophosphate was omitted. This battery wasevaluated, and the results thereof are shown in Table 15.

Comparative Example 3 for Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that the 0.05mol/L lithium salt of cyclic 1,2-perfluoroethanedisulfonylimide, whichis a cyclic disulfonylimide salt, was omitted. This battery wasevaluated, and the results thereof are shown in Table 15.

Comparative Example 4 for Nonaqueous Electrolyte 6

A nonaqueous-electrolyte secondary battery was produced in the samemanner as in Example 1 of Nonaqueous Electrolyte 6, except that anonaqueous electrolyte was obtained by dissolving 1 mol/L sufficientlydried LiPF₆ and 1 part by weight of vinylene carbonate in a mixture ofethylene carbonate and ethyl methyl carbonate (volume ratio, 3:7) in adry argon atmosphere. This battery was evaluated, and the resultsthereof are shown in Table 15.

TABLE 15 Results of evaluation of high- Presence or temperaturestorability Cyclic Monofluorophosphate and/or absence of StorageResidual Recovery disulfonylimide salt difluorophosphate vinylene swellcapacity capacity (mol/L) (wt %) carbonate (mL) (%) (%) Example 1lithium salt of cyclic 1,2- lithium difluorophosphate absent 0.14 80 85perfloroethanedisulfonylimide (0.5) (0.05) Example 2 lithium salt ofcyclic 1,2- lithium difluorophosphate absent 0.19 83 86perfloroethanedisulfonylimide (0.5) (0.1) Example 3 lithium salt ofcyclic 1,2- lithium difluorophosphate absent 0.14 78 82perfloroethanedisulfonylimide (0.5) (0.01) Example 4 lithium salt ofcyclic 1,2- lithium difluorophosphate absent 0.15 81 85perfloropropanedisulfonylimide (0.5) (0.05) Example 5 sodium salt ofcyclic 1,2- lithium difluorophosphate absent 0.16 81 84perfloroethanedisulfonylimide (0.5) (0.05) Example 6 lithium salt ofcyclic 1,2- lithium difluorophosphate absent 0.17 75 81perfloroethanedisulfonylimide (0.1) (0.05) Example 7 lithium salt ofcyclic 1,2- lithium difluorophosphate absent 0.13 80 86perfloroethanedisulfonylimide (1.0) (0.05) Example 8 lithium salt ofcyclic 1,2- sodium difluorophosphate absent 0.16 80 86perfloroethanedisulfonylimide (0.5) (0.05) Example 9 lithium salt ofcyclic dilithium absent 0.15 78 84 1,2- monofluorophosphateperfloroethanedisulfonylimide (0.5) (0.05) Example 10 lithium salt ofcyclic 1,2- lithium difluorophosphate present 0.27 82 86perfloroethanedisulfonylimide (0.5) (0.05) Comparative — — absent 0.2762 67 Example 1 Comparative lithium salt of cyclic 1,2- — absent 0.33 6975 Example 2 perfloroethanedisulfonylimide (0.05) Comparative — lithiumdifluorophosphate absent 0.20 67 78 Example 3 (0.5) Comparative — —present 0.42 67 83 Example 4

The following is apparent from Table 15. The nonaqueous-electrolytesecondary batteries produced using the nonaqueous electrolytes of theinvention, which contained at least one cyclic disulfonylimide saltrepresented by general formula (8) and further contained amonofluorophosphate and/or a difluorophosphate (Example 1 of NonaqueousElectrolyte 6 to Example 10 of Nonaqueous Electrolyte 6), were inhibitedfrom swelling during high-temperature storage and from deteriorating inbattery characteristics represented by residual capacity and recoverycapacity, as compared with the nonaqueous-electrolyte secondarybatteries produced using the nonaqueous electrolytes containing one ofthese compounds (Comparative Example 2 for Nonaqueous Electrolyte 6 andComparative Example 3 for Nonaqueous Electrolyte 6) or using anonaqueous electrolyte containing neither of those compounds(Comparative Example 1 for Nonaqueous Electrolyte 6).

Furthermore, even when compared with Comparative Example 2 forNonaqueous Electrolyte 6 and Comparative Example 3 for NonaqueousElectrolyte 6, in which the nonaqueous electrolytes contained onlyeither of a cyclic disulfonylimide salt represented by general formula(8) and a monofluorophosphate and/or difluorophosphate, Example 1 ofNonaqueous Electrolyte 6 to Example 10 of Nonaqueous Electrolyte 6, inwhich the nonaqueous electrolytes contained both of these compounds,were ascertained to have been improved in both inhibition of swellingduring high-temperature storage and inhibition of deterioration inbattery characteristics. In addition, as apparent from a comparisonbetween Example 10 of Nonaqueous Electrolyte 6 and Comparative Example 4for Nonaqueous Electrolyte 6, the same effect was observed also in thecase of using a nonaqueous electrolyte containing vinylene carbonate,which is an example of the specific carbonate.

INDUSTRIAL APPLICABILITY

<Nonaqueous Electrolytes 1 and 2 and Nonaqueous-Electrolyte SecondaryBatteries 1 and 2>

According to nonaqueous electrolytes 1 and 2 of the invention,nonaqueous-electrolyte secondary batteries having a high energy densitycan be produced in which the electrolytes are inhibited from decomposingand which are inhibited from deteriorating when used in ahigh-temperature environment. These batteries further have high capacityand are excellent in storability and cycle characteristics.Consequently, these batteries are suitable for use in various fieldswhere nonaqueous-electrolyte secondary batteries are used, e.g., in thefield of electronic appliances.

<Nonaqueous Electrolyte 3 and Nonaqueous-Electrolyte Secondary Battery3>

According to nonaqueous electrolyte 3 of the invention, a nonaqueouselectrolyte and a nonaqueous-electrolyte secondary battery can beproduced which are excellent in cycle characteristics, storability,inhibition of gas evolution during continuous charge, and batterycharacteristics. Consequently, this battery is suitable for use invarious fields where nonaqueous-electrolyte secondary batteries areused, e.g., in the field of electronic appliances.

<Nonaqueous Electrolyte 4 and Nonaqueous-Electrolyte Secondary Battery4>

Nonaqueous-electrolyte secondary battery 4, which employs nonaqueouselectrolyte 4 of the invention, retains high capacity and is excellentin safety, etc. This battery can hence be used in various knownapplications.

<Nonaqueous Electrolyte 5 and Nonaqueous-Electrolyte Secondary Battery5>

Nonaqueous-electrolyte secondary battery 5, which employs nonaqueouselectrolyte 5 of the invention, retains high capacity and is excellentin continuous-charge characteristics, etc. This battery can hence beused in various known applications.

<Nonaqueous Electrolyte 6 and Nonaqueous-Electrolyte Secondary Battery6>

According to nonaqueous electrolyte 6 of the invention, anonaqueous-electrolyte secondary battery having a high energy densitycan be produced in which the nonaqueous electrolyte is inhibited fromdecomposing and which is inhibited from deteriorating when used in ahigh-temperature environment. This battery further has high capacity andis excellent in storability and cycle characteristics. Consequently,this battery is suitable for use in various fields wherenonaqueous-electrolyte secondary batteries are used, e.g., in the fieldof electronic appliances.

Applications of nonaqueous electrolytes 1 to 6 for secondary batteriesand nonaqueous-electrolyte secondary batteries 1 to 6 of the inventionare not particularly limited, and these electrolytes and batteries canbe used in various known applications. Examples thereof include notebookpersonal computers, pen-input personal computers, mobile personalcomputers, electronic-book players, portable telephones, portablefacsimile telegraphs, portable copiers, portable printers, headphonestereos, video movie cameras, liquid-crystal TVs, handy cleaners,portable CD players, mini-disk players, transceivers, electronicpocketbooks, electronic calculators, memory cards, portable taperecorders, radios, backup power sources, motors, motor vehicles,motorbikes, bicycles fitted with a motor, bicycles, illuminators, toys,game machines, clocks and watches, power tools, stroboscopes, andcameras, and the like.

This application is based on the following Japanese patent applications,the entire contents thereof being herein incorporated as a disclosure ofthe description of the invention.

-   Nonaqueous electrolyte 1: Application No. 2007-116442 (filing date:    Apr. 26, 2007)-   Nonaqueous electrolyte 2: Application No. 2007-116445 (filing date:    Apr. 26, 2007)-   Nonaqueous electrolyte 3: Application No. 2007-116450 (filing date:    Apr. 26, 2007)-   Nonaqueous electrolyte 4: Application No. 2007-111961 (filing date:    Apr. 20, 2007)-   Nonaqueous electrolyte 5: Application No. 2007-099274 (filing date:    Apr. 5, 2007)-   Nonaqueous electrolyte 6: Application No. 2007-111931 (filing date:    Apr. 20, 2007)

The invention claimed is:
 1. A nonaqueous electrolyte, comprising: (A)an electrolyte; (B) a nonaqueous solvent dissolving the electrolyte; (C)a salt of a monofluorophosphate ion of formula PO₃F, a difluorophosphateion of formula PO₂F₂, or a mixture thereof with at least one metal ionselected from a metal of Group 1 of the periodic table selected fromlithium, sodium, potassium, and cesium, a metal of Group 2 of theperiodic table selected from magnesium, calcium, strontium, and bariumand a metal of Group 13 of the periodic table selected from aluminum,gallium, indium, and thallium; and (D) at least one compound selectedfrom the group consisting of:

wherein R¹, R², and R³ are each independently a fluorine atom, an alkylgroup comprising 1-12 carbon atoms and optionally substituted with afluorine atom, or an alkoxy group comprising 1-12 carbon atoms andoptionally substituted with a fluorine atom; (ii) a nitrile compound;(iii) an isocyanate compound; (iv) a phosphazene compound; (v) adisulfonic acid ester compound; (vi) a sulfide compound; (vii) adisulfide compound; (viii) an acid anhydride; (ix) a lactone compoundcomprising a substituent in the α-position; and (x) a compoundcomprising a carbon-carbon triple bond.
 2. The nonaqueous electrolyte ofclaim 1, wherein a total content of the compound (D) is from 0.01% to25% by mass, based on a total mass of the nonaqueous electrolyte.
 3. Thenonaqueous electrolyte of claim 1, wherein a total content of thecompound (D) is from 0.01% to 10% by mass, based on a total mass of thenonaqueous electrolyte.
 4. The nonaqueous electrolyte of claim 1,wherein a total content of the compound (D) is from 0.01% to 5% by mass,based on a total mass of the nonaqueous electrolyte.
 5. The nonaqueouselectrolyte of claim 1, wherein a total content of the compound (D) isfrom 0.1% to 5% by mass, based on a total mass of the nonaqueouselectrolyte.
 6. The nonaqueous electrolyte of claim 1, wherein a totalcontent of the salt (C) is from 0.001% to 5% by mass, based on a totalmass of the nonaqueous electrolyte.
 7. The nonaqueous electrolyte ofclaim 1, wherein a total content of the salt (C) is from 0.01% to 4% bymass, based on a total mass of the nonaqueous electrolyte.
 8. Thenonaqueous electrolyte of claim 1, wherein a total content of the salt(C) is from 0.05% to 3% by mass, based on a total mass of the nonaqueouselectrolyte.
 9. The nonaqueous electrolyte of claim 1, wherein the salt(C) is Li⁺PO₇F₂.
 10. The nonaqueous electrolyte of claim 1, wherein thesalt (C) is Na⁺PO₂F₂.
 11. The nonaqueous electrolyte of claim 1, whereinthe salt (C) is Mg²⁺(PO₂F₂ ⁻)₂.
 12. A nonaqueous-electrolyte secondarybattery comprising: a negative electrode and a positive electrode, whichare capable of occluding/releasing lithium ions; and the nonaqueouselectrolyte of claim
 1. 13. The nonaqueous-electrolyte secondary batteryof claim 12, wherein the negative electrode comprises a carbonaceousmaterial.
 14. The nonaqueous-electrolyte secondary battery of claim 12,wherein the negative electrode comprises a negative-electrode activematerial comprising at least one selected from the group consisting of asilicon atom, a tin atom, and a lead atom.